After the diagnosis of pregnancy is made, it is imperative to determine the duration of pregnancy and the estimated date of confinement (EDC).
Normally, human pregnancy lasts 280 days or 40 weeks (9 calendar months or 10 lunar months) from the last normal menstrual period (LNMP). This may also be calculated as 266 days or 38 weeks from the last ovulation in a normal 28-day cycle.
[...] If a ring of bubbles appears in the second vial after 30 seconds of vigorous shaking, an L/S ratio of 2 or greater can be assumed. Bubbles in the 1:1 mixture but not in the second vial mean that the fetus is at a borderline stage of development and the pregnancy should be allowed to continue if possible. Ultrasonography Multiple early prenatal ultrasound examinations are most accurate in diagnosing fetal maturity. However, a biparietal diameter of 9.8 cm or more late in gestation is usually indicative of fetal maturity. [...]
[...] Estimated Date of Confinement (Nägele's Rule) The EDC can be determined mathematically using Nägele's rule: Subtract 3 months from the month of the LNMP, and add 7 to the first day of the LNMP. Example: With an LNMP of July 14, the EDC is April 21. This rule is based on a normal 28-day cycle. In women with a longer proliferative phase, add to the first day of the LNMP the usual 7 days plus the number of days that the cycle extends beyond 28 days. [...]
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