-DATING PREGNANCY FROM OVULATION DATE
The calculation of the EDD from the ovulation day is the most accurate way to date a pregnancy as conception takes place within 24 hours of ovulation.
DATING PREGNANCY FROM OVULATION DATE
Going by the Naegele’s rule, if ovulation occurs on the 14th day of a regular 28 day menstrual cycle and the LMP is exactly 14 days before the ovulation day, putting in perspective that the EDD is 280 days from the the first day of the LMP, then by subtracting 14 days from 280 (266 days), the EDD is exactly 266 days from the ovulation date i.e. EDD = ovulation date + 266 days. Therefore, women who are able to track thier ovulation date correctly and those who have ultrasound scan tracking of their follicles followed by timed intercourse or intra uterine insemination of semen at ovulation, can calclate their EDD by adding 266 days to their ovulation date.
Similarly, the calulation of a woman’s current pregnancy age can be calculated from the ovulation date using the same principle as above which assume that ovulation occur on the 14th day of each menstrual cycle and that the LMP is 14 days or two weeks before the ovulation date. Hence, given a particular ovulation date for any pregnancy, the first day of the LMP can be calculated by subtracting 14 days from the ovulation date and from this newly calculated LMP, the pregnancy age using the Naegele’s rule can be calculated.
For example a pregnant woman who had intra uterine insemination and ovulated on the 15/02/2018 will have a calculated LMP of 01/02/18 and an EDD of 08/11/18.
On the other hand, for pregnancies conceived by IVF, both the age of the pregnancy, the EDD and the supposed LMP can be calculated from the date of embryo transfer and the age of the embryo at transfer. Thus by adding 14 to the age of the embryo at transfer (e.g 14 + 5 for an embryo transferred at the age of 5 days), the LMP can be calculated by subtracting the calculated sum from the date of embryo transfer. The calculated date of the supposed LMP can then be used to calculate the pregnancy age and the EDD using the Naegele’s rule as shown in the example below.
For example, to calculate the current age of pregnany of a woman who had a 3 day old embryo achieved by IVF, transferred on the 20/02/2018, subtract 14 + 3 (17) from 20/02/2018 to get the new LMP (03/02/18) and subtract the new LMP from the current day of examination. Hence if the woman was being assessed on 03/05/2018, her pregnancy date would be 13 weeks from the calculated LMP while her EDD would be 10/11/18 (03+7/ 02 + 9/18 = 03/11/18).
1. Ovulation tracking is known only to a few percentage of women who alone can reap the benefit of its accuracy. It is also a bit tedious and requires some level of commitment. As daunting as it may seem, I have met a few women in the antenatal clinic who dazed me with the accuracy with which they were able to track their ovulation date. If you want to learn how to track your ovulation day accurately, read the various articles on ovulation on this website or CHAT WITH OUR CONSULTANTS.
2. Women with irregular cycles may find it almost impossible to track their ovulation day, as ovulation here is occasional and is unpredictable. Hence, using the ovulation day for the purpose of dating pregnancy is almost impossible and any pregnancy in women with irregular cycles can only be accurately dated with an early scan and not by the LMP or by the ovulation date. To know if your cycles are regular, please read up NORMAL AND ABNORMAL MENSTRUAL CYCLES and to look up possible causes of irregular cycles and their management, read up all articles on irregular menstrual cycles or kindly CHAT WITH OUR CONSULTANTS.
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