Pregnancy Week by Week: What Actually Happens (Without the Fluff)
Most pregnancy guides bury useful information under paragraphs of feelings and affirmations. Here is what is actually happening to you and your baby, week by week, in plain language.
Pregnancy lasts 40 weeks from the first day of your last menstrual period, which means weeks 1-2 are counted before conception even occurs. Actual embryonic development starts at week 3 (fertilization) and the pregnancy test turns positive around week 4-5 when hCG levels are high enough to detect. This dating system is confusing but universal — every doctor, app, and guide counts from the LMP, so understanding it prevents a constant 2-week mental adjustment.
First Trimester (Weeks 1-12)
Week 4-5: the embryo implants in the uterine wall. This is when some women notice light spotting (implantation bleeding), which is often mistaken for a light period. A home pregnancy test is reliable from week 5. Week 6: the heart begins beating — detectable on ultrasound but too faint to hear with a stethoscope. Week 8: all major organs have begun forming. The embryo is the size of a raspberry. Week 10: morning sickness peaks for most women, though "morning" is a misnomer — nausea can hit at any time. Week 12: risk of miscarriage drops significantly. Many couples wait until this milestone to share the news.
Second Trimester (Weeks 13-27)
Week 16: you may feel the first flutters of movement (quickening), though first-time mothers often do not recognize them until week 20. Week 18-22: the anatomy scan — a detailed ultrasound that checks every organ system and can reveal the sex. This is the ultrasound most parents remember. Week 24: the viability threshold — with NICU care, about 40-70% of babies born at 24 weeks survive, though outcomes improve dramatically with each additional week in the womb.
Third Trimester (Weeks 28-40)
Week 28: the baby opens and closes its eyes, can hear external sounds, and responds to light. Week 32: most babies rotate to the head-down position. Week 36: the baby is considered "early term" and would likely do well if born, though 39-40 weeks is optimal. Week 37-38: weekly prenatal visits begin. Week 39-40: full term. Only 5% of babies arrive on their exact due date — most arrive between 38 and 42 weeks.
Calculate your due date and see your personalized milestone timeline with our due date calculator — enter your last period date and it shows every key milestone with your specific dates.