The fertilization age (also called embryonic age and later fetal age) is the time from the fertilization.
It usually occurs within a day of ovulation, which, in turn, occurs on average 14.6 days after the beginning of the preceding menstruation (LMP).
When people discuss how far along in pregnancy someone is, they tend to do so in general terms: “She’s in the first trimester” or “She’s four months along.” However, many people have only a vague idea of what those phrases really mean.
Medical professionals use a standard set of up to three methods to date pregnancies: last menstrual period, ultrasound, and a physical exam.
Five dating methods: LMP, FH, US and their combinations, were assessed against the actual day of delivery (ADD).
The actual variability between gestational age as estimated from the beginning of the last menstrual period (without the use of any additional method mentioned in previous section) is substantially larger because of uncertainty which menstrual cycle gave rise to the pregnancy.Ultrasonography (US) in the 1st, or early 2nd trimester, is highly reproducible8 and widely used for dating, since early biological variability of fetal biometry is minimal.9 In the past, certain LMP was used for dating as long as the GA was within 7, 10 or 14 days of the estimate of GA by US,10 but now 1st, or 2nd trimester, US is increasingly recommended as the single dating method because of its smaller error rate.1 14 The current policy in the Western Cape Province of South Africa (SA) provides for a routine US examination between 18 - 23 weeks of the clinically estimated GA for low-risk pregnancies since this reduces the number of presumptive post- and pre-term deliveries as well as the number of referrals to a higher level of care for suspected deviations in fetal growth.15 The approximately 34% of women who typically present at 23 weeks16 do not routinely receive US.Pregnancy dating is based on a pragmatic guideline incorporating information from the LMP, FH and early US (if available).17 The accuracy of this guideline and the clinical value of late US-based GA dating have not been assessed. Okland I, Gjessing HK, Grøttum P, Eggebø TM, Eik-Nes SH. two traditional sample-based models: validation on 9046 ultrasound examinations. The 21 Best Pregnancy i Phone & Android Apps of 2013 Calculating your due date isn’t an exact science.Very few women actually deliver on their due date, so while it’s important to have an idea of when your baby will be born, try not to get too attached to the exact date.The other way to calculate your due date is to use a pregnancy wheel. It’s very easy to estimate your due date if you have access to a pregnancy wheel. When you line up that date with the indicator, the wheel will display your due date. Luckily, there are ways to figure out your due date when you can't remember the first day of your LMP.