The significance of oral contraceptives in causing chromosome anomalies in spontaneous abortions

Maternal use of oral contraceptives and risk of birth defects in Denmark: prospective, nationwide cohort study

STUDY QUESTION

Is oral contraceptive use around the time of pregnancy onset associated with an increased risk of major birth defects?

METHODS

In a prospective observational cohort study, data on oral contraceptive use and major birth defects were collected among 880,694 live births from Danish registries between 1997 and 2011. We conservatively assumed that oral contraceptive exposure lasted up to the most recently filled prescription. The main outcome measure was the number of major birth defects throughout one year follow-up (defined according to the European Surveillance of Congenital Anomalies classification). Logistic regression estimated prevalence odds ratios of any major birth defect as well as categories of birth defect subgroups.

STUDY ANSWER AND LIMITATIONS

Prevalence of major birth defects (per 1000 births) was consistent across each oral contraceptive exposure group (25.1, never users; 25.0, use >3 months before pregnancy onset (reference group); 24.9, use 0-3 months before pregnancy onset (that is, recent use); 24.8, use after pregnancy onset). No increase in prevalence of major birth defects was seen with oral contraceptive exposure among women with recent use before pregnancy (prevalence odds ratio 0.98 (95% confidence interval 0.93 to 1.03)) or use after pregnancy onset (0.95 (0.84 to 1.08)), compared with the reference group. There was also no increase in prevalence of any birth defect subgroup (for example, limb defects). It is unknown whether women took oral contraceptives up to the date of their most recently filled prescription. Also, the rarity of birth defects made disaggregation of the results difficult. Residual confounding was possible, and the analysis lacked information on folate, one of the proposed mechanisms.

WHAT THIS STUDY ADDS

Oral contraceptive exposure just before or during pregnancy does not appear to be associated with an increased risk of major birth defects.

FUNDING, COMPETING INTERESTS, DATA SHARING

BMC was funded by the Harvard T H Chan School of Public Health's Maternal Health Task Force and Department of Epidemiology Rose Traveling Fellowship; training grant T32HD060454 in reproductive, perinatal, and paediatric epidemiology and award F32HD084000 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development; and grant T32CA09001 from the National Cancer Institute. The authors have no competing interests or additional data to share.

Human germline and somatic cells have similar TP53 and Kirsten-RAS gene single base mutation frequencies

Understanding the risk of offspring inheriting rare mutations, and the frequencies at which these mutations are present in germ cells can be explored with direct analysis of human semen samples. The present work utilized the ultrasensitive PCR/RE/LCR mutation assay to detect, identify and determine the prevalence single base substitution mutations in the TP53 and KRAS genes in human sperm. Four disease-associated base sites in the TP53 and KRAS genes, three of which are known to be heritable to live, term offspring, were studied in sperm from eleven human semen specimens. Eight of the specimens (73%) displayed single base substitution mutations, and 30% of all base sites tested were found to harbor mutations ranging in prevalence from 1 x 10(-6) to 1 x 10(-5) wild type sperm. These germ cell single base substitution mutation frequencies are very similar to somatic tissue TP53 and KRAS mutation frequencies. Equivalent single base mutation frequencies in both germ and somatic cells suggest that there is no unusual selection or mutation protective process operating premeiotically in the germline, and that a selection bias at the level of sperm viability, conception, early cleavage, implantation, and/or embryogenesis operates to exclude the majority of these TP53 mutations and all of the activating KRAS mutations.

Recurrent Fetal Aneuploidy and Recurrent Miscarriage

OBJECTIVE

Some investigators have found a high frequency of abortus aneuploidy in women with recurrent miscarriage, suggesting the possibility of recurrent aneuploidy as a cause of recurrent miscarriage. Others contend that aneuploidy is not a cause of recurrent miscarriage. The purpose of this study was to investigate the relationship between fetal aneuploidy and recurrent miscarriage by estimating whether fetal aneuploidy is more common in patients with recurrent miscarriage than in patients with sporadic miscarriage

METHODS

Recurrent miscarriage cases (n = 135) included women who had a subsequent miscarriage in which an abortus karyotype was obtained. Controls (n = 150) were patients experiencing a sporadic miscarriage who had fetal karyotypes performed as part of a study to assess the utility of abortus tissue for transplantation. Karyotype analysis was performed using standard G-banding techniques.

RESULTS

Abortuses from 122 cases and 133 controls were successfully karyotyped. Thirty-one (25.4%) abortuses from cases and 56 (42.1%) from controls were aneuploid (odds ratio 0.47, 95% confidence interval 0.27-0.80). Aneuploid abortuses occurred in 20% of cases and 25% of controls, aged 20-29 years, 19% of cases and 24% of controls, aged 30-34 years, 35% of cases and 47% of controls, aged 35-39 years, and 50% of both cases and controls, aged 40 years or older (not significant). Of 30 cases in whom 2 or more miscarriages were karyotyped, 3 (10%) had aneuploidy in each abortus.

CONCLUSION

In our population of recurrent miscarriage patients, abortus aneuploidy occurred significantly less often than in sporadic miscarriages. The rate of aneuploidy in this study was considerably lower than reported in other studies. If recurrent aneuploidy contributes to recurrent miscarriage, it does so in only a small number of patients.

LEVEL OF EVIDENCE

II-2

Inducibility of chromosome aberrations by steroid hormones in cultured Chinese hamster ovary cells

The effect of steroid hormones on the chromosomes of cultured Chinese hamster ovary (CHO) cells was studied. It was noticed that estradiol-17 beta, estrone, estriol and ethynyl estradiol were effective in producing various types of chromosome aberrations. The percentage of these abnormalities increased with increasing concentrations of steroids used. The importance of detailed and long-term investigations on the influence of these compounds on mammalian chromosomes is discussed.

Chromosomal abnormalities in the Kaiser-Permanente Birth Defects Study, with special reference to contraceptive use around the time of conception

Chromosomal abnormalities were studied in 33,551 abortions and births to women whose contraceptive histories had been recorded at their first antenatal visit in 1975-1977. Chromosome examinations were performed exclusively on clinical grounds. There were 45 de novo abnormalities detected (1.34/1,000); three of them were detected at amniocentesis. Trisomy 21 was observed in 27 cases (0.80/1,000), trisomy 18 in nine (0.27), other trisomies in three (0.09), and translocations or deletions in five (0.15). One case of triploidy and six cases of inherited abnormalities were detected. There were no significant racial variations. No increase in risk for chromosomal abnormalities was found among women who had used oral contraceptives prior to becoming pregnant or among women who experienced oral contraceptive breakthrough pregnancies. Two cases of trisomy 18 were observed among the 814 deliveries following oral contraceptive breakthrough conceptions (2.46/1,000), two cases of trisomy 21 occurred in 338 births following failures of rhythm contraception (5.92/1,000), and no cases of trisomy 21 or 18 among the 1,569 women using spermicides at the time of conception.

The chromosomal effects of the oral contraceptive

A general review of reports on the chromosomal effects of oral contraceptive has been undertaken, and it is quite apparent that there is a scarcity of literature on these very important investigations. Also, those that have been undertaken, cannot be properly assessed on account of, one supposes, subjects' background and lack of numbers, differences in techniques and, above all, the small number of metaphases analyzed. Apart from the report by Mills and colleagues [16], none of the reports mentioned exogenous agents to which the subjects might have been exposed, especially in cases where there has been an increased frequency of chromosomal aberrations. All these considerations must be taken into account for, as yet, the reports are too conflicting to 'indict' the oral contraceptive as having chromosome-breaking properties.

Contraceptives and the conceptus. II. Sex of the fetus and neonate after oral contraceptive use

The sex distribution of 1421 induced abortuses and 2986 newborn infants was correlated with maternal contraceptive histories. Sex of abortuses was determined by chromosome and sex chromatin analyses. No statistically significant differences (P Greater Than 10) were found between the sex ratios either of the fetuses or of the infants of women who used hormonal (oral) contraceptives as compared to those of noncontraceptive controls nor between the induced and newborn series. Also, no correlation was found between sex of the conceptus and total duration of oral contraceptive use, or interval between termination of contraceptive use and conception. Therefore, if the use of low dose oral hormonal contraceptives has an effect on the sex of subsequent offspring, it is likely to be small since the 95% confidence interval for the sex ratios for the oral contraceptive groups divided by the sex ratios of the noncontraceptive group (odds ratio) are 0.80 to 1.22 for induced abortions, and 0.82 to 1.10 for newborns. These conclusions are not in agreement with some earlier reports, generally of small samples, but they are consistent with the results of Rothman and Liess (1976) from a sample of 6109 infants born to oral contraceptive users.

Epidemiology of trisomy 21: population, peri- and antenatal data

In Down's syndrome, incidence of 1 0/00-2 0/00 have been reported in chromosomal surveys of consecutive liveborn infants and in population studies. Much attention has been focused on the influence of the decline in mean maternal age on the incidence of Down's syndrome. Decline in incidence and unchanged incidences have been reported. For mothers over 35 years old, a rise in incidence has been found in recent years in some societies. Environmental factors or seasonal fluctation might cause this trend. Data from antenatal diagnosis show a 30% higher incidence of Down's syndrome for age groups over 35 than population studies do. Late abortions of trisomic fetuses, a high perinatal mortality, and a small rise in incidence for higher maternal ages in recent years may account for this fact. With the growing tendency toward younger maternal age at childbirth, paternal factors also have to be considered. Between 10% and 30% paternal failures have been found by nondisjunction studies applying chromosomal variants. The rate of paternal failures may reflect environmental influences and young maternal age distribution. Recently, an increase in trisomy 21 children of mothers in the age group 30-39 who are pill users has been observed. The positive sex ratio of male Down's syndrome patients has been reversed in patients born to mothers using hormonal contraception. The mortality rate, in Down's syndrome is still high in early childhood, especially perinatally and in the 1st year of life. For the late 1940s in Denmark, newborns with Down's syndrome had a mortality rate of 53% in the 1st year of life. In the late 1960s and early 1970s, the rate had fallen to 22%. The main causes of death were congenital heart disease in connection with infections, especially pneumonia. Cot death might be more common in Down's syndrome. After the age of 1 year, mortality is reduced considerably and more and more cases will survive early childhood and live to rather old ages.

Sister-chromatid exchanges in oral contraceptive users

The effect of the use of an oral contraceptive on the frequency of sister-chromatid exchanges (SCEs) was investigated. Oral contraceptive users showed significantly higher mean SCE per cell compared with both normal and pregnant women. This result obviously means an increased mutagenic environment in these cells--due either to the pill itself or to a metabolite(s).

Are hormonal contraceptives teratogenic?

The widespread use of hormonal contraceptives for a prolonged time in women during the child-bearing period necessitates that appropriate precautions be taken to ensure safety for the patient as well as for her progeny. Hormonal administration during or prior to pregnancy may be potentially teratogenic. Although there have been many reports during the last decade, it has been very difficult to document conclusively such a relationship. Over-all, it seems that hormonal use prior to pregnancy does not lead to an increase in the frequency of chromosomal aberrations or of congenital malformations. The use of certain hormones during pregnancy, on the other hand, may lead to an increase in the incidence of congenital malformations, probably in the genetically predisposed fetus. In view of this concept hormonal contraceptives should not be used to treat threatened abortion, and their use as a pregnancy test should be abandoned. Since the question of the safety of the inadvertent administration of pills during early pregnancy has not been resolved, the mother should be informed of the potential risks.