Norgestimate/ethinyl oestradiol was compared with another oral birth control pill that contained norethidrone acetate/ethinyl oestradiol. However the two pills differed in the type of progestin.

"The incidence of breakthrough bleeding or spotting was significantly lower in the majority of cycles for women who received the norgestimate/ ethinyl oestradiol formulation compared with those who received the norethidrone acetate/ ethinyl oestradiol formulation," said Raymond Hampton, MD, associate professor of obstetrics and gynaecology, Texas Tech University Health Sciences Center School of Medicine, Odessa, Texas, United States.

The retrospective analysis a randomised, multicentre study involved 1,506 women who were assigned to birth control with norgestimate/ethinyl oestradiol contraceptive and 1,057 women who were assigned to norethidrone acetate/ethinyl oestradiol.

In the studies, at all patient weight levels, breakthrough bleeding occurred less frequently in patients taking the norgestimate-containing contraceptive, Dr. Hampton reported at his poster presentation on May 9, 2007.

In women who weighed less than 123 lbs (55.5 kg), rates of breakthrough bleeding were 11% with the norgestimate product and 25.4% with the norethidrone progestin. In women weighing 124-155 lbs (55.5-70.3 kg), rates of breakthrough bleeding were 10% and 22.5%, respectively. In women weighing more than 155 lbs (70.3 kg), breakthrough bleeding rates were 10% and 18.3%, respectively.

For each comparison, the difference reached statistical significance at the P <.01 level, Dr. Hampton said.

There were similar results seen when the comparisons were made by age, Dr. Hampton said.

"Breakthrough bleeding is a bothersome side effect of using the Pill," he said. "These data demonstrate that women using Ortho Tri-Cyclen Lo, an effective low-dose combination birth-control pill, have significantly less breakthrough bleeding regardless of weight or age."


[Presentation title: Bleeding Patterns with Mono- and Triphasic Low-dose Ethinyl Estradiol Combined Oral Contraceptives. Abstract 5 (May 9)]

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