Official Statistics

Sex ratios at birth in the United Kingdom, 2015 to 2019: report

Published 14 October 2021

Executive summary

Aim

This report provides statistics on the analysis of male to female birth sex ratios in the United Kingdom using the most recent data for the period 2015 to 2019. This report was previously published for Great Britain until last year where it was extended to include Northern Ireland.

The purpose of these Official Statistics is to update and inform the public and Parliament on whether or not there is evidence for sex selective abortions happening at scale within specific communities in the United Kingdom. Data is sourced from birth registration data in England, Wales, Scotland and Northern Ireland. This analysis uses a generally accepted birth sex ratio upper limit of 107 (see paragraph 1.15) that is, we are looking for birth sex ratios with significantly more than 107 males born for every 100 females within a group.

Where the ratio of males to females for a particular ethnicity or mother’s country of origin is significantly greater than 107 (after adjusting for multiple testing and the birth order of the child), this may indicate that people in this group have been involved in sex selective abortions. A lower birth sex ratio limit is not used, as we are not investigating if there are many more females born than males born in the United Kingdom.

This analysis has been repeated annually since 2013 and over this time, there has been no evidence for sex selective abortions occurring in the UK. We want to better understand how this publication is used, and by who, to be able to assess the usefulness of this publication going forward. Please see the further information section for more details.

Key findings from 2015 to 2019 data

This report presents statistics on the analysis of male to female birth sex ratios in the United Kingdom for the period 2015 to 2019:

• this analysis of birth sex ratios finds no evidence for sex selective abortions occurring in the United Kingdom over the period 2015 to 2019
• there were 3.7 million births registered in the United Kingdom in this period with a ratio of males to females of 105.5, below the accepted upper limit of 107. (See table 1: results)
• latest analyses by ethnicity of the child and mother’s country of origin for overall birth sex ratios, and by birth order, shows no ratio was found to be significantly higher than a male to female birth sex ratio of 107. (See table 2 and 3 in accompanying spreadsheets.)

1. Background

1.1 The Department of Health and Social Care (DHSC) made a commitment to publish birth sex ratio analysis annually, in line with the recommendation of the Council of Europe Parliamentary Assembly that member states should ‘collect the sex ratio at birth, monitor its development and take prompt action to tackle possible imbalances’ and ‘encourage research on sex ratios at birth among specific communities’. If more males than females are being born than is expected, this could imply some pregnancies are being terminated with an abortion due to the sex of the fetus. This process is known as a sex selective abortion. However, a number of factors can influence the sex of a child including maternal and paternal age, coital rates, number of children and sex of previous children.

The legal context

1.2 Concern has been raised in some countries about the occurrence of sex selective abortions^{[footnote 1]},^{[footnote 2]}.

1.3 Sex is not itself a lawful ground for abortion in England, Wales and Scotland (Abortion Act 1967). Department of Health and Social Care guidance, in May 2014, states that abortion on the grounds of sex alone is illegal (see point 25 in the Guidance in Relation to Requirements of the Abortion ACT 1967) (PDF, 137KB).

1.4 However, under the Abortion Act, it is lawful to abort a fetus where 2 registered medical practitioners (RMPs) (doctors) are of the opinion, formed in good faith, “that there is a substantial risk that if the child were born it would suffer from such physical or mental abnormalities as to be seriously handicapped.” This would be classed as a Ground E abortion. There are some serious conditions which are known to be related to a person’s sex.

1.5 From 31 March 2020 a new framework for access to abortion services for Northern Ireland came into force. As with England, Wales and Scotland, sex is not itself a lawful ground for abortions in Northern Ireland.

1.6 In early 2015 the Serious Crime Act contained a requirement that the Secretary of State should arrange for an assessment to be made, within 6 months of Royal Assent, of the evidence for sex-related abortions occurring. A report was subsequently laid before Parliament in August 2015, which contained the assessment of evidence of terminations of pregnancy being undertaken on the grounds of the sex of the fetus, and a statement and explanation of why the Secretary of State for Health considered a formal plan under sub-section (3) (a) of the clause was not required.

Identifying the sex of a fetus with technology

1.7 Antenatal sexing of the fetus is not a routine part of antenatal care. Scans are undertaken to support the clinical care of the mother and unborn baby such as:

• the number of fetuses
• the age of the fetus
• screening for fetal anomalies

It is usually only possible to identify the sex of a baby at the second ultrasound scan, which takes place at around 18 to 21 weeks gestation. Disclosing the sex of a fetus is a local decision, adhering to local policies, and should be based on clinical judgment about the certainty of the assessment and the individual circumstances of each case.

1.8 The introduction of new and emerging technologies (such as Non-Invasive Prenatal Testing (NIPT) which is currently available in private clinics and on the internet) provide further context from which the monitoring of birth sex ratios needs to be considered. NIPT is available on the NHS depending on eligibility criteria but will not include assessment of the sex of the fetus.^{[footnote 3]}

1.9 The majority of abortions take place in the first trimester of pregnancy (94% up to 12 weeks; 71% up to 7 weeks gestation, Abortion statistics for England and Wales 2020). The majority of abortions are therefore taking place nearly 2 months before most women could have been told the sex of the fetus in the antenatal screening pathway. It is acknowledged though that some people may seek information on sex using other methods such as tests available on the internet or in private clinics. However, data is not available on the extent to which other methods of sex determination may be being used. See Appendix A for further information on abortions by gestation and ethnicity.

Trends in birth sex ratios

1.10 Within large populations, we can expect the birth sex ratio to vary, due to external factors^{[footnote 4]} including wars and economic crises. Figure 1 shows the fluctuation within the United Kingdom since 1908. The chart shows that the birth sex ratio has never been above 107 over that period. The minimum ratio was 103.5 in 1914 and the maximum ratio was 106.7 in 1973. The male to female birth sex ratio has been consistently around 105 since 1980.

Figure 1: live male births per 100 live female births, England and Wales, Scotland and Northern Ireland

Source: Office for National Statistics, National Records of Scotland and Northern Ireland Statistics and Research Agency.

1.11 The issue of sex ratios of new-born babies is the subject of numerous academic articles, where there is a range of evidence. A 2011 World Health Organisation report stated a biologically normal sex ratio at birth ranges from 102 to 106 male births, per 100 female births,^{[footnote 5]} although other studies have stated that 105 or lower is a more “normal” ratio of males to females^{[footnote 6]}. Evidence suggests that a number of factors can influence the sex of a child, including maternal and paternal age, coital rates, number of children and sex of previous children^{[footnote 7]}. It is important to note that the interaction between factors that could influence the sex of the child has not been controlled for or taken into account in this analysis.

1.12 For this publication a birth sex ratio upper limit of 107 males to 100 females is used as a threshold for comparisons. This is based on a review of available literature^{[footnote 8]} advice from academic experts and on examination of data on birth sex ratios in more developed countries.

Calculations and statistical tests used

1.13 The aim of this analysis is to investigate if any of the birth sex ratios considered are statistically significantly higher than 107, that is, if any group has statistically significantly more than 107 males born for every 100 females.

1.14 Birth sex ratios above the 107 threshold do occur, but could be due to chance, rather than due to a real difference. Statistical significance testing is carried out to determine whether any differences observed between the birth sex ratios and the 107 threshold are likely to be “real” or whether they are consistent with chance fluctuations.

1.15 This publication uses a number of methodologically approved techniques to test whether ratios over 107 are statistically significant. The first stage of the process is to calculate the probability (‘p values’) that the differences observed could arise by chance as opposed to there being a real difference. We have used the common acceptable level of 5% significance level in this analysis, which means that a statistically significant result is found for any p values less than 0.05 (5%).

1.16 However, this methodology presents some difficulties when there are many tests involved. For example, the ‘mother’s country of origin’ analysis involved testing the significance level for 174 countries and 5 birth orders, theoretically equivalent to 870 statistical tests (In fact, 814 tests were carried out as 56 countries in the unknown birth order category had no data available). With so many tests, it would be expected that some results appear statistically significant due to chance alone. Even when there was no real difference from a ratio of 107, on average, a 5% significance level means that 1 in 20 results would be found to be significant. When applying this across these mother’s country of origin tests there is a high chance of a ‘false positive’ result, therefore inferring evidence about sex selective abortions incorrectly.

1.17 In order to address this issue known as the ‘multiple testing problem’, a statistical technique called the Benjamini-Hochberg procedure was applied using p values already calculated as part of our method to assess statistical significance. In addition to this procedure, the Storey technique is also used to estimate false positive discovery rate as a form of sensitivity analysis. The application of these techniques is discussed in detail in the technical guidance.

Limitations of the analysis

1.18 Using birth registration data to calculate birth sex ratios is an indirect method for investigating evidence for sex selective abortions.

1.19 The relatively small number of births within many of the groups in this analysis are such that large differences between birth sex ratios and the expected upper limit of 107 would need to be observed for the ratio to be identified as statistically significantly higher than the expected upper limit of 107. Therefore, evidence would only be identified through this means if sex selection were taking place on a significant scale.

1.20 Any differences in the birth sex ratios seen could be due to a number of factors, not just sex selective abortions. There is evidence that paternal and maternal age, coital rates and the number and sex of previous children can influence the sex of a child.

2. Results

Coverage of this analysis

2.1 This report presents statistics on the analysis of male to female birth sex ratios in the United Kingdom for the period 2015 to 2019. This report was previously published for Great Britain until last year where it was extended to include Northern Ireland.

2.2 Sex ratios are examined overall and by birth order (first born, second born, and so on) for:

• all mothers of babies born in 2015 to 2019 for the United Kingdom
• the mother’s country of origin for babies born in 2015 to 2019 for the United Kingdom
• ethnicity of child born in 2015 to 2019 for England and Wales

All births

2.3 In the period 2015 to 2019, there were 3.7 million live births in the United Kingdom and an overall ratio of males to females of 105.5 which is below the upper limit of 107. (Analysis covered countries where the total number of births for 2015 to 2019 was 100 or more to ensure adequate sample sizes, so excluding some countries).

2.4 The birth sex ratio did not vary significantly across the different birth orders with a ratio between 105 and 107 males to 100 females (see table 1 below).

Table 1: birth sex ratios by birth order, United Kingdom, 2015 to 2019

Birth order	Number of births	Birth sex ratio
All births	3,748,399	105.5
First born	1,559,723	105.9
Second born	1,317,686	105.3
Third born or more	859,743	105.2
Unknown	11,247	106.8

Unknown birth order represents those babies whose birth order was unknown.

Births by ethnicity of the child

2.5 Data on ethnicity of the child is not available for Scotland and Northern Ireland, therefore this component of the analysis is limited to England and Wales.

2.6 There were 3.4 million births included in the analysis of birth sex ratios by ethnicity of the child and birth order, for England and Wales. The majority of births in England and Wales were for children in the White British ethnic group (62% of stated ethnicities).

2.7 An analysis of birth sex ratios by the ethnicity of the child for England and Wales both for overall birth sex ratio and by birth order, showed no ratio to be significantly higher than 107. (See table 3 in accompanying spreadsheets.)

2.8 Although some birth sex ratios were higher than 107, such as third born or later babies of Indian ethnicity, following the statistical testing, no ethnicity and birth order were found to be statistically significant.

Figure 2: birth sex ratios by ethnicity: England and Wales, 2015 to 2019

Figure 3: birth sex ratio by ethnicity and birth order: England and Wales, 2015 to 2019

2.9 When interpreting the birth sex ratios (table 3), it is important to keep in mind that this analysis covers 9 ethnic groups, in line with the ethnic groupings used by the Office for National Statistics, for 5 categories of birth order (all, first born, second born, third born or later, and unknown birth order). We would therefore expect to see high birth sex ratios for some groups simply as a result of random variation and small sample sizes.

Births by mother’s country of origin

2.10 The majority of births in the United Kingdom were to mothers born in England, Wales, Scotland and Northern Ireland (73%). This analysis focuses on the mother’s country of origin for the 27% (representing 1,010,707 births) of babies born to mothers from countries outside of England, Wales, Scotland or Northern Ireland.

2.11 The analysis for the United Kingdom on the overall birth sex ratio and birth order by the mother’s country of origin, showed no result to be significantly higher than 107.

2.12 It is important to note that the analysis of births by mother’s country of origin did produce some birth sex ratios higher than 107 (see table 2 in accompanying spreadsheets). For example, Benin’s birth sex ratio for second childbirth is 152.9 males to 100 females. However, this is likely the result of random variance on a small sample size of 43 births. Further analysis was conducted on the data using the Benjamini-Hochberg and Storey statistical techniques and these techniques indicated that no birth sex ratio was statistically significantly higher than 107 and therefore, not indicative of sex selective abortions.

2.13 Table 2 (in accompanying spreadsheets) shows the birth sex ratios for all the countries included in the analysis. When interpreting the birth sex ratios in table 2, it is important to keep in mind that this analysis covers 174 country of origin groups for 5 categories of birth order (all, first born, second born, third born or later, and unknown birth order). We would therefore expect to see high birth sex ratios for some groups simply as a result of random variation and small sample sizes. To illustrate, during 2015 to 2019 for women born in Djibouti, there were 26 babies who were the first born with a birth sex ratio of 85.7 while 35 babies were the second born with a birth sex ratio of 218.2. However, this has not produced a statistically significant result. This wide variation exists, particularly where sample sizes are smaller (see figure 4 below).

Figure 4: plot of male to female birth sex ratio by mother’s country of origin: All births, United Kingdom, 2015 to 2019

2.14 The greater variation in countries with lower numbers of live births is shown in figure 4 in relation to the unadjusted birth sex ratios and compared to the 107 males to 100 females ratio used as the threshold for comparisons. Over half the countries (66%) are below the 107 ratio threshold, with most of those that are higher having low sample sizes, for example Luxembourg and Paraguay where the ratio is 126 and 140 males to 100 females respectively. Similar variation is seen below the 107 line, with Barbados where there were 78 males born for every 100 females. As noted above, when testing using the Benjamini-Hochberg technique, there were no countries found to be statistically significantly higher than the 107 ratio threshold.

Abortions by gestation and ethnicity

2.15 To supplement the birth sex ratio analysis, further analysis has been done to investigate the relationship between gestation (and thus when sex can be identified) and abortion rates, by ethnic group of the woman. This shows that the number of abortions vary by ethnicity of the woman, gestation period and number of previous abortions. The majority of abortions occur before the women would know the sex of the fetus. See Annex A for further detail.

Conclusion

2.16 Following extensive statistical testing, this analysis of birth sex ratios finds no evidence for sex selective abortions occurring in the United Kingdom over the period 2015 to 2019. No evidence for sex selective abortions has been found since these statistics were first published.

Appendix A: abortions by gestations and ethnicity

Data on the sex of the fetus at an abortion is not available, which is why birth registrations data are used in this analysis. We can however analyse abortions data by ethnicity of the mother and gestation to provide wider context around the birth sex ratio analysis. Any evidence for unusual birth sex ratios might imply sex selective abortions were taking place in the population.

This section adds some additional context on abortions by gestation and ethnicity from the annual abortion statistics publication:

Abortion statistics for England and Wales 2020

This appendix refers to abortions for residents of England and Wales in 2020.

All abortions, by gestation

The total number of abortions for residents of England and Wales in 2020 was 209,917. This was an increase of 1% from 2019, and the highest number recorded since the Abortion Act was introduced. The majority of abortions took place in the early stages of pregnancy: 94% up to and including 12 weeks, and 71% up to and including 7 weeks gestation; NHS antenatal sexing of a fetus typically takes place much later in the pregnancy at 18 to 21 weeks gestation and chart 1 shows 98% of abortions took place at 17 weeks gestation or less. The majority of abortions are therefore taking place nearly 2 months before most women could have been told the sex of the fetus in the antenatal screening pathway. It is acknowledged though that some people may seek information on sex using other methods such as tests available on the internet or in private clinics. However, data is not available on the extent to which other methods of sex determination may be being used.

Chart 1: proportion of abortions by gestation week, England and Wales, 2020

All abortions by ethnic group of woman

Ethnicity was recorded on 95% of the forms received for 2020. Of all ethnicities recorded in the Abortions Statistics publication, 77% were reported as White, 9% as Asian or Asian British and 7% as Black or Black British, 4% as mixed and 2% as Any other ethnic group (see chart 2).

Chart 2: abortion statistics split by ethnic group of woman, England and Wales, 2020

All abortions, by gestation and ethnic group of woman

There are variations between the gestation period of an abortion when comparing different ethnicities. The proportion of abortions before 17 weeks range from 97% to 99% depending on the ethnic group of the woman. For abortions carried out before 12 weeks the range between different ethnic groups is from 90% to 94%, with a wider range for abortions carried out before 7 weeks from 51% to 57% depending on the ethnic group of the woman.

Table 2: abortions by gestation period and ethnic group, residents of England and Wales, 2020

Ethnic group of woman	Total number of abortions	Less than 7 weeks gestation	7 to 11 weeks gestation	12 to 16 weeks gestation	17 to 21 weeks gestation	22 weeks and over gestation
All ethnic groups	209,917	54%	38%	5%	2%	1%
White – British	134,649	54%	39%	5%	2%	1%
White – Irish	1,286	53%	39%	5%	2%	0%
White – any other white background	18,284	52%	38%	7%	2%	1%
Mixed – white and Black Caribbean	3,877	53%	40%	5%	2%	0%
Mixed – white and Asian	1,259	57%	36%	5%	1%	0%
Mixed – white and Black African	1,118	54%	40%	4%	2%	0%
Mixed – any other	2,649	55%	38%	4%	2%	1%
Asian or Asian British – Indian	6,820	55%	36%	5%	3%	1%
Asian or Asian British – Pakistani	4,516	56%	35%	6%	3%	1%
Asian or Asian British – Bangladeshi	1,818	53%	40%	5%	2%	1%
Asian – any other Asian background	4,038	55%	38%	4%	2%	1%
Black or Black British – African	9,141	55%	37%	5%	2%	1%
Black or Black British – Caribbean	4,018	53%	39%	6%	2%	1%
Black or Black British – Any other	1,590	55%	37%	6%	2%	1%
Chinese	1,145	53%	39%	4%	2%	1%
Any other ethnic group	3,286	53%	38%	6%	2%	1%
Not known or not stated	10,423	51%	39%	7%	2%	1%

For abortions under 7 weeks, Asian or Asian British-Pakistani women have the highest proportion (56%). The ethnic group with the lowest proportion of abortions under 7 weeks gestation was: Not known/not stated (51%).

Abortions over 17 weeks account for 3% of all abortions. There is some variation across ethnicities for this gestation. Asian or Asian British-Indian and Asian or Asian British-Pakistani have 4% of abortions over 17 weeks. Women who have stated their ethnicity as Mixed-White and Asian have 1% of abortions over 17 weeks.

Repeat abortions and ethnic group

Of all abortions in 2020, 42% had previously had one or more abortions. Again, among women who have had a previous abortion, there was variation across ethnic groups.

48% of Black or Mixed ethnicity women having abortions in 2020 had previously had at least one abortion, compared with 34% of Chinese or other ethnic group.

Table 3: percentage of women who had one, two, three or more previous abortions, by ethnic group of the woman, England and Wales, 2020

Ethnic group of woman	No previous abortions	One previous abortion	Two previous abortions	Three or more previous abortions	Total
All ethnicities	58%	30%	9%	3%	100%
White	58%	30%	9%	3%	100%
Mixed	52%	32%	11%	5%	100%
Asian	66%	26%	6%	2%	100%
Black	52%	33%	11%	5%	100%
Chinese or other	66%	24%	7%	3%	100%
Not known or not stated	61%	27%	8%	4%	100%

Conclusion

This section shows that abortions vary by ethnicity of the mother, gestation period and whether the mother has had previous abortions.

Further information

As part of the ongoing development of this publication, we are reviewing its content and methodology. If you have any feedback relating to this publication or are a user of these statistics and would like to be consulted about its content or methodology, please get in touch at birthratios@dhsc.gov.uk

Enquiries

Enquiries about the data or requests for further information should be addressed to:

Birth Ratio Statistics
Department of Health and Social Care
39 Victoria Street
Westminster
London
SW1H OEU

E-mail: birthratios@dhsc.gov.uk

1. Hesketh, T., & Xing, Z. W. (2006). Abnormal sex ratios in human populations: causes and consequences. Proceedings of the National Academy of Sciences, 103(36), 13271-13275. ↩

2. Chahnazarian, A. (1988). Determinants of the sex ratio at birth: Review of recent literature. Social biology, 35(3-4), 214-235. ↩

3. In this test a small blood sample is taken from the mother’s arm. The UK National Screening Committee made a recommendation to use NIPT, a contingent test in the NHS Fetal Anomaly Screening Programme only for Trisomy 13,18 and 21 and not for any other genetic marker, including sex. (A trisomy is a disorder characterised by an additional chromosome). ↩

4. Helle, S., Helama, S., & Lertola, K. (2009). Evolutionary ecology of human birth sex ratio under the compound influence of climate change, famine, economic crises and wars. Journal of Animal Ecology, 78(6), 1226-1233. ↩

5. World Health Organization. (2011). Preventing gender-biased sex selection: an interagency statement OHCHR, UNFPA, UNICEF, UN Women and WHO. ↩

6. Hesketh, T., & Xing, Z. W. (2006). Abnormal sex ratios in human populations: causes and consequences. Proceedings of the National Academy of Sciences, 103(36), 13271-13275. ↩

7. Jacobsen, R., Møller, H., & Mouritsen, A. (1999). Natural variation in the human sex ratio. Human reproduction, 14(12), 3120-3125. ↩

8. Chahnazarian, A. (1988). Determinants of the sex ratio at birth: Review of recent literature. Social biology, 35(3-4), 214-235. ↩