Timing of Intercourse, Ovulation and Conception
Frederick R. Jelovsek MD
"When is the best time to check a pregnancy test if you have regular cycles and are trying to get pregnant? Is it true the earlier the test turns positive the less likely it is to have a miscarriage? " Anon
Many women who are trying to conceive want to learn when ovulation and implantation occur and what are usual miscarriage or pregnancy loss rates. Quite often the numbers women are give
n are based on averages, theoretical numbers and sometimes just plain guesses because it is such a difficult topic to scientifically investigate. New data comes available periodically but it is not always promptly and widely disseminated even on the Net.
When does implantation take place?
One such relatively recent study tells us that implantation does not always take place on day 7 after ovulation. In fact it very rarely does. This study by AJ Wilcox accurately determined the day of implantation by very sensitive pregnancy test (HCG) measurement compared to ovulation.
HCG hormone starts being produced when the pregnancy implants into the uterine lining. The findings in normal women trying to conceive included:
- first appearance of HCG (implantation) occurred 6-12 days after ovulation
- 84% of the pregnancies implanted on days 8-10 after ovulation
- early pregnancy loss increased with later implantation -
implantation early pregnancy loss rate
- 13% by day 9
- 26% on day 10
- 52% on day 11
- 86% on day 12 or more
Overall the total pregnancy loss up to 6 weeks was 25%. Now that seems very high to most people but keep in mind many of these pregnancy losses occurred so early that women often were not aware they were even pregnant.
The normal early pregnancy loss rate that most women know about is 15-18% of clinically recognized pregnancies so almost 40% of all pregnancy loss is unrecognized.
When is the best time to have intercourse in order to get pregnant?
Wilcox had also performed previous work in 1995 (2) which demonstrated that pregnancy only occurs if intercourse occurs within the 6 days prior to and including ovulation. Intercourse after the day of ovulation does not result in pregnancy.
The probability of conception ranged from 10% when intercourse occurred five days before ovulation to 33% when it occurred on the day of ovulation itself.
This is the data that suggests the best timing of intercourse in order to conceive is day 10, 12, 14 and 16 (in case of late ovulation) of a 28 day cycle or days -4, -2, 0, +2 in relation to expected ovulation in the case of cycles different than 28 days.