Summary
Highlights
Pregnancy typically spans 9 months or 40 weeks, segmented into three trimesters. The first trimester is from week 1 to week 12, the second from week 13 to 27, and the third from week 28 until birth.
A fertilized egg develops into an embryo in the womb. By week 9, it becomes a fetus, with most organs, including the heart, forming. By 12 weeks, the baby is about 6 cm long. The umbilical cord connects the baby to the placenta, providing oxygen and nutrients and removing waste.
During the second trimester, the baby's sex organs develop, and other organs mature. The baby swallows amniotic fluid, and kidneys begin to function, passing small amounts of urine. The baby can hear and is covered in fine hair called lanugo. The mother will start to feel the baby's movements, which will become stronger and more noticeable. Braxton Hicks contractions may begin around 20 weeks.
In the third trimester, the baby's lungs mature, eyes open and close, and fingernails and hair grow. Fat stores increase in preparation for birth. Towards the end of pregnancy, the baby drops into the pelvis, preparing for delivery.