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1.3% of abortions occur after 21 weeks of pregnancy in the US. Although it is very uncommon, women undergoing surgical abortion after this gestational age sometimes give birth to a fetus that may survive briefly. [55] [56] [57] The periviable period is considered to be between 20 and 25 weeks gestation. [58]
Gestational age: 5 weeks and 0 days until 5 weeks and 6 days old. 36–42 days from last menstruation. Embryonic age: Week nr 4. 3 weeks old. 22–28 days from fertilization. The embryo measures 4 mm (1 ⁄ 8 in) in length and begins to curve into a C shape. The heart bulges, further develops, and begins to beat in a regular rhythm.
The third trimester is defined as starting, between the beginning of week 28 (27 weeks + 0 days of GA) [37] or beginning of week 29 (28 weeks + 0 days of GA). [4] It lasts until childbirth . Timeline of pregnancy, including (from top to bottom): Trimesters, embryo/fetus development, gestational age in weeks and months, viability and maturity stages
The first ten weeks of gestational age is the period of embryogenesis and together with the first three weeks of prenatal development make up the first trimester of pregnancy. From the 10th week of gestation (8th week of development), the developing embryo is called a fetus.
Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third trimester is 29/30th–42nd week. [ 6 ]
Also starting about week 12, the thoracic diaphragm moves up and down as if the fetus were breathing, but this movement disappears about week 16 and does not resume until the third trimester. [16] Movements such as kicking continue, and the mother usually feels movement for the first time, an event called quickening, during the fifth month. [17]
The mean pregnancy length has been estimated to be 283.4 days of gestational age as timed from the first day of the last menstrual period and 280.6 days when retrospectively estimated by obstetric ultrasound measurement of the fetal biparietal diameter (BPD) in the second trimester. [12]
The newer integrated screen (formerly called F.A.S.T.E.R for First And Second Trimester Early Results) can be done at 10 plus weeks to 13 plus weeks with an ultrasound of the fetal neck (thicker nuchal skin correlates with higher risk of Down syndrome being present) and two chemicals (analytes), pregnancy-associated plasma protein A and human ...