Stages of Pregnancy

Fetal Growth Stages

The first trimester (or first 14 weeks) is an important time in your developing baby’s life. It’s a time of fast growth and development. It’s also a time when the fetus is most at risk from hazards such as smoking, alcohol, drugs, infections, and X‑rays.


4 weeks 6 mm (1/4 in.)	8 weeks 22-24 mm (1 in.)	12 weeks 9 cm (3 1/2 in.)

The second trimester is the time between 15 and 27 weeks gestation. During this time your developing baby’s brain grows a lot. The developing baby is still too small to live outside of your body.


16 weeks 16 cm (6 1/2 in.)	20 weeks 25 cm (10 in.)

The third trimester is the time between 28 weeks and your baby’s birth. The closer to full term or 40 weeks gestation your baby is, the better your baby is able to cope with birth and to life outside your body. Forty weeks gestation is the date estimated to be your due date.

If your baby is born before 37 weeks gestation, it is considered to be preterm (born early). If your baby is born after 42 weeks gestation, it is said to be post term. There is a higher risk of illness and death in babies born too early or too late.