Oral Contraceptives in Pregnancy and Breastfeeding

Risk Factor: XM
Class: Hormones / Progestogens

Contents of this page:
Fetal Risk Summary
Breast Feeding Summary
Questions and Answers

Fetal Risk Summary

Oral contraceptives contain a 19-nortestosterone progestin and a synthetic estrogen (see Mestranol, Norethindrone, Norethynodrel, Ethinyl Estradiol, Progesterone, Hydroxyprogesterone, Ethisterone). Because oral contraceptives are primarily combination products, it is difficult to separate entirely the fetal effects of progestogens and estrogens. Two groups of investigators have reviewed the effects of these hormones on the fetus (133 References) (1,2). Several potential problems were discussed: congenital heart defects, central nervous system defects, limb reduction malformations, general malformations, and modified development of sexual organs. Except for the latter category, no firm evidence has appeared that establishes a causal relationship between oral contraceptives and various congenital anomalies. The acronym VACTERL (Vertebral, Anal, Cardiac, Tracheal, Esophageal, Renal or Radial, and Limb) has been used to describe the fetal malformations produced by oral contraceptives or the related hormonal pregnancy test preparations (no longer available in the United States) (2,3). The use of this acronym should probably be abandoned in favor of more conventional terminology as a large variety of malformations have been reported with estrogen-progestogencontaining products (1,2,3,4,5,6,7,8,9,10 and 11). The Population Council estimates that, even if the study findings for VACTERL malformations are accurate, such abnormalities would occur in only 0.07% of the pregnancies exposed to oral contraceptives (12). Some reviewers have concluded that the risk to the fetus for nongenital malformations after in utero exposure to these agents is small, if indeed it exists at all (2).

In contrast to the above, the effect of estrogens and some synthetic progestogens on the development of the sexual organs is well established (2). Masculinization of the female infant has been associated with norethindrone, norethynodrel, hydroxyprogesterone, medroxyprogesterone, and diethylstilbestrol (2,13,14). The incidence of masculinization of female infants exposed to synthetic progestogens is reported to be approximately 0.3% (15). Pseudohermaphroditism in the male infant is not a problem, because of the low doses of estrogen employed in oral contraceptives (14).

Increased serum bilirubin in neonates of mothers taking oral contraceptives or progestogens before and after conception has been observed (16). Icterus occasionally reached clinically significant levels in infants whose mothers were exposed to the progestogens.

Concern that oral contraceptives may be a risk factor for preeclampsia has been suggested on the basis of the known effects of oral contraceptives on blood pressure (17). However, a retrospective controlled review of 341 patients found no association between this effect and the drugs (17).

Possible interactions between oral contraceptives and tetracycline, rifampin, ampicillin, or chloramphenicol resulting in pregnancy have been reported (18,19,20,21,22,23,24 and 25). The mechanism for this interaction may involve the interruption of the enterohepatic circulation of contraceptive steroids by inhibiting gut hydrolysis of steroid conjugates, resulting in lower concentrations of circulating steroids.

Breast Feeding Summary

Use of oral contraceptives during lactation has been associated with shortened duration of lactation, decreased infant weight gain, decreased milk production, and decreased composition of nitrogen and protein content of milk (26,27,28 and 29). The American Academy of Pediatrics has reviewed this subject (30) (37 References). Although the magnitude of these changes is low, the changes in milk production and composition may be of nutritional importance in malnourished mothers.

In general, progestin-only contraceptives demonstrate no consistent alteration of breast milk composition, volume, or duration of lactation (30). The composition and volume of breast milk will vary considerably even in the absence of steroidal contraceptives (29). Both estrogens and progestins cross into milk. An infant consuming 600 mL of breast milk daily from a mother using contraceptives containing 50 g of ethinyl estradiol will probably receive a daily dose in the range of 10 ng (30). This is in the same range as the amount of natural estradiol received by infants of mothers not using oral contraceptives. Progestins also pass into breast milk, although naturally occurring progestins have not been identified. One study estimated 0.03, 0.15, and 0.3 g of d-norgestrel/600 mL of milk from mothers receiving 30, 150, and 250 g of the drug, respectively (31). A milk:plasma ratio of 0.15 for norgestrel was calculated by the authors (31). A ratio of 0.16 has been calculated for lynestrenol (31,32).

Reports of adverse effects are lacking except for one child with mild breast tenderness and hypertrophy who was exposed to large doses of estrogen (30). If breast feeding is desired, the lowest effective dose of oral contraceptives should be chosen. Infant weight gain should be monitored, and the possible need for nutritional supplements should be considered. The American Academy of Pediatrics considers combination oral contraceptives to be compatible with breast feeding (33).


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