silver (04/02/83)
It's true that it is difficult to determine the time of conception accurately. It's indicative of the state of the art that the standard charts (and little cardboard wheels!) used by doctors for dating pregnancies are calibrated from the LNP (last natural period). However, I knew that when I posted the first article, and assumed that the Enc. Brit. information was based on "careful studies". I still hope someone knows why the information they state doesn't look like a nice bell curve, though. In our case, we are fortunate to know the exact time of conception. My wife, just for grins, started taking her BBT (basal body temperature) the very month she conceived, and produced a classic chart -- though we didn't know that till later. Good thing she did, too, or we'd be off by ten days! The doctor explained that from ovulation to next period is almost always exactly 14 days. It's the time from period to ovulation that varies (in her case, ten days too long), which is why LNP is often inaccurate. I highly recommend BBT if you are even THINKING of getting pregnant. It's easy, can remove much of the doubt about dating, and reduces the need for ultrasound, etc. Alan