Pregnancy Week by Week

During weeks 1–13, all major organs and body systems begin forming. The heart starts beating around week 6. By week 8, the embryo officially becomes a fetus. By week 12, fingers, toes, and facial features are distinct, and the risk of miscarriage drops significantly after this point.

Nausea and vomiting (commonly called "morning sickness," though it can strike at any time) usually begins around week 6, peaks at weeks 8–10, and resolves for most women by week 14. About 1 in 10 women experience it into the second trimester. Severe cases (hyperemesis gravidarum) may need medical treatment.

The baby's sex may be visible on ultrasound from around week 16, but the anatomy scan (weeks 18–22) gives a more reliable determination. Cell-free DNA blood tests (NIPT) can detect biological sex as early as week 10 with high accuracy.

The anatomy scan (also called the Level 2 or mid-pregnancy ultrasound) is typically performed between weeks 18–22. It checks for structural abnormalities in the brain, heart, spine, limbs, and organs; measures the baby's size; assesses placental position; and estimates amniotic fluid levels.

"Full term" is defined as 39–40 weeks of gestation. "Early term" is 37–38 weeks, and "late term" is 41 weeks. Babies born before 37 weeks are preterm. While 37 weeks is often called "term," research shows that babies benefit from staying in the womb until at least 39 weeks when possible. Only 5% of babies are born on their exact due date.

During weeks 27–40, the baby gains most of their birth weight and the brain develops rapidly. You may notice more pronounced kicks, Braxton Hicks contractions, back pain, and increased fatigue. The baby typically moves into a head-down position by week 36. Most organs are fully mature by week 37–39.