Escape ovulation in women due to the missing of low dose combination oral contraceptive pills.

Chowdhury V; Joshi UM, Gopalkrishna K; Betrabet S; Mehta S; Saxena BN
Contraception. 1980 Sep; 22(3):241-7.

It is generally believed that in women taking combined (OCs) oral contraceptives, the risk of pregnancy increases if a pill is missed. A study was undertaken in healthy, normally menstruating women who were given low dose combination OCs containing norethisterone acetate (NET Ac) 1 mg and ethinyl estradiol (EE2) 30 mcg. In the control group, 10 women were asked to take the pills daily for 21 days beginning on day 5 of the menstrual cycle. In the study group, consisting of similar women who had been sterilized, they were asked to 'miss the pills' on 2 consecutive days anywhere between day 5 and day 17 of the menstrual cycle. 35 women were 'made to miss' the pills in the 1st treatment cycle and another 19 were asked to do so in the 4th treatment cycle. Cervical mucus and lateral vaginal wall smears were studied 3 times/week. Endometrial biopsy was done on day 23 + or - 2. 2 serum (P) progesterone levels were determined between day 22 and day 25 of the cycle. In the control group, whereas only 1 subject showed P levels (> 4 ng/ml) suggestive of ovulatory cycle, the endometrial biopsy tissue available in 8 of 10 subjects showed no secretory effect. However, in the study group escape ovulation as indicated by P levels (> 4 ng/ml) was observed in 10 of 35 women in the 1st treatment cycle group and 5 of 19 women in the 4th treatment cycle group. Again, in all those women, the endometrial biopsies did not show any secretory effect and the cervical mucus was poor throughout the cycle. Data suggest that though missing of the low dose OCs may result in escape ovulation in some women, the pharmacological effects of the pills on the endometrium and cervical mucus may continue to provide them with contraceptive protection in a manner similar to that reported in women using low dose gestagen only pills. Therefore, it is likely that the relative degree of contraceptive protection in women occasionally missing the low dose OCs would be reduced, as compared to that observed in women taking the pills on a regular daily basis. (Authors' modified)

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