1999 Jun 10;340(23 1796-9.
You might also like, how is a pregnancy due date calculated?
303, February 2014 Society of Obstetricians and Gynaecologists of Canada.Acog Practice Bulletin.Doppler Ultrasonography, the fetal heart can be heard using Doppler ultrasound by 10 to 12 weeks in most patients.Sometimes special cases, such as women who are artificially inseminated or use in vitro fertilization, are able to know the exact date of their conception.Natl Vital Stat Rep.Sign up for, start4Life's pregnancy and baby emails for expert advice, videos and tips on pregnancy, birth and beyond.Use The Conception Calculator to estimate probable conception dates from Birth, LMP and Due dates.Since conception is based off the regularity of the womens cycle, factors such as stress can change these cycles monthly and make it difficult to pinpoint an exact conception time.To find your due date, enter the date of the first day of your last period, and click 'show your due date' - the calculator will do the rest.Greater than 10 days from 16 0/7 weeks to 21 6/7 weeks by LMP.The conception calculator will give you a range of days in which conception may have occurred.Some women, even with regular period cycles, may have varying ovulation cycles.2009 Feb;113(2 Pt 1 451-61.J Obstet Gynaecol Can.Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.Prevention of Rh D alloimmunization.Possible Dates of Conception?Number 9, October 1999 (replaces Technical Bulletin Number 188, January kostenlose Kontakt sex 1994).Determining the Date of Conception, because the human egg is capable of fertilization for only 12 to 24 hours after ovulation the date of ovulation may be taken as being the date of conception.
Effects on the probability of conception, survival of the pregnancy, and sex of the baby.

Ultrasound uses the size of the fetus to determine the gestational age (the time elapsed since the the first day of the last menstrual period).
101: Ultrasonography in pregnancy.