becoming pregnant right after coming off oral contraceptive

Posted by Jane on April 17, 1999 at 14:41:33
This is my first month without using oral contraceptives; my husband and I are using another form of birth control.
I would very much like to know what are the possible complications if I get pregnant during my first cycle off oral contraceptives.  
I have read that it is advised to wait 2 or 3 months before becoming pregnant in order to improve gestational dating.  Why is gestational dating so important?  
Other than not being able to easily date a pregancy, are there other disadvantages to becoming pregnant so soon after coming off oral contraceptives?
Thank you.

Posted by hfhs.md.db on April 17, 1999 at 17:00:51
I do not believe that my experience or the medical literature supports the concept that it is necessary to wait "2 to 3 months" after stopping oral contraception (OC). There are no additional reported complications that I am aware of that occur in women conceiving on the first pill-free cycle.
The "gestational dating" scenario has to do with the practice of dating pregnancies using the last menstrual period (LMP). We date pregnancies using the first day of the LMP rather than the scientifically more valid conception date (think about it--using the LMP means that the in first two weeks of "pregnancy" a woman is not pregnant at all!) because the LMP is a readily identifiable date for most women. The assumption is that in a 28 day cycle (another fallacy; very few women have perfectly 28 day cycles), the conception would occur 14 days after the first day of the LMP. However, in defense of tradition, the LMP dating practice is certainly accurate for most situations.
This relationship does not necessarily hold for a women conceiving when the LMP is a OC withdrawal rather than a spontaneous period, because typically women do not ovulate/conceive exactly 14 days after an OC withdrawal (most of the time, ovulation is delayed for a variable length of time). Therefore,using the LMP rule (also called Naegle's rule) will be less accurate than usual.
The way around all of this is simply to obtain an ultrasonographic evaluation early in the pregnancy (preferably in the first trimester). This is a highly accurate way to "date" a pregnancy. Therefore, I do not routinely suggest to patients that it is necessary to wait for 2 to 3 spontaneous menses before trying to conceive.
Incidently, as I mentioned in a recent response to a posting about the "due date (EDC)", the due date is simply a reference point that caregivers use to approximate the duration of the pregnancy. Very few women actually deliver on their due date. As I said before, "the baby will come when it is ready to come".