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The effect of deliberate omission of a phased formulation pill, TrinordiolR (ethinyl estradiol 30 μg + levonorgestrel 50μg: 6 tablets; ethinyl estradiol 40 μg + levonorgestrel 75 μg : 5 tablets; ethinyl estradiol 30 μg + levonorgestrel 125 μg: 10 tablets) or a low-dose, combined, oral contraceptive pill, MicrogynonR (ethinyl estradiol 30 μg + levonorgestrel 150 μg: 21 tablets) on the hypothalamo-pituitary-ovarian axis were studied.
Thirty-six women were recruited to the study and divided equally between the two types of pill. Medication was begun on the 8th pill-free day of the cycle and continued for 7 days (Group 1), 14 days (Group 2) or 21 days (Group 3). Levels of FSH, LH, estradiol (E2) and progesterone (P) were measured in plasma on alternate days during the final week of pill therapy, and daily for the 7 days after stopping the pill.
For the first 2 weeks of pill therapy, follicular activity, as judged by plasma levels of E2, was greater in women taking Trinordiol than in those taking Microgynon, but was similar in both groups by the third week of pill treatment. Five women taking Trinordiol (2 in Group 1 and 3 in Group 2) had plasma levels of E2 in excess of 500 pmol/1 whilst taking the pills, but this level of follicular activity was maintained in only three of these women in the seven ‘pill-free’ days. None of the women taking Microgynon had levels of E2 above 500 pmol/1 whilst taking the pills and only 1 patient achieved this degree of follicular activity after stopping the tablets.
One woman who had taken 7 days of Trinordiol (Group 1) showed a rise of plasma levels of P to 6.8 nmol/1, but luteinization did not occur in any of the remaining 35 women who took Trinordiol or Microgynon.
These findings suggest that follicular activity is less completely suppressed by Trinordiol than Microgynon, at least in the first 2 weeks of pill therapy, but that normal ovulation is still a rare event in the week after cessation of either of these pills, even if only 7 days of medication have been taken.
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Accepted: November 5, 1986
Received: September 8, 1986
© 1986 Published by Elsevier Inc.