Dating pregnancy conception calculator
Number 4, May 1999 (replaces educational bulletin Number 147, October 1990). Number 9, October 1999 (replaces Technical Bulletin Number 188, January 1994). The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study BMJ 2000; 321: 1259-1262. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. Timing of sexual intercourse in relation to ovulation.
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).
303, February 2014 Society of Obstetricians and Gynaecologists of Canada.
Multifetal gestations: twin, triplet, and higher-order multifetal pregnancies.
The Society of Obstetricians and Gynaecologists of Canada recommends the earliest ultrasound with a crown rump length equivalent to at least 7 weeks (or 10 mm) should be used to determine the gestational age .
The American College of Obstetricians and Gynecologists recommends that ultrasound-established dates should take preference over menstrual dates when the discrepancy between ultrasound dating and LMP is "Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; they need to be guided by careful consideration of the entire clinical picture and may require closer surveillance, including repeat ultrasonography to ensure appropriate interval growth." . Birth weight from pregnancies dated by ultrasonography in a multicultural British population.