Written by : Dr.M.D.Mazumdar, MD
Normal pregnancy lasts for 280 days or 40 weeks. A baby who is born after 42 weeks is termed a postmature baby and one who is born before 37 weeks is a preterm baby.
Pregnancy is divided into three more or less equal stages, known as trimesters. Each of these trimesters correlate with different stages of fetal development - the first trimester is associated more with development of the fetal organs, the second trimester is associated with growth and enlargement of the developed organs and the third trimester is associated with growth plus physiological maturity. Physiological maturity means that the organs can now function more or less like an adult's- relasing enzymes or hormones etc.
The first trimester lasts from the first day of the last missed perod to the end of 13 weeks.
The second trimester lasts from the beginning of the 14th week to the end of the 27th week.
The third trimester lasts from the beginning of the 28th week to the end of the 40th week of pregnancy.
The expected date of delivery or the expected due date (EDD) is the date when the baby is expected to deliver. It is calculated by counting 9 months plus 7 days from the first day of the last missed period. This calculation s accurate only if a woman has a regular menstrual cycle of 28 +/- 2 days. If the cycle is longer, the extra days need to be added to the total duration.
For a woman who has an irregular menstrual cycle, an ultrasound in early pregnancy is more accurate.
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