Pregnancy Milestones: A Trimester-by-Trimester Guide
Follow key pregnancy milestones from the first trimester through delivery, including fetal development, important tests, and what to expect.
First Trimester (Weeks 1–12)
The first trimester is a period of rapid development. By week 5, the embryo's heart begins to beat. By week 8, all major organs have started forming, and the embryo is now called a fetus. Common symptoms for the mother include nausea, fatigue, breast tenderness, and frequent urination. Key prenatal tests during this period include blood work, an ultrasound to confirm the pregnancy and estimate the due date, and optional first-trimester screening for chromosomal conditions.
Second Trimester (Weeks 13–26)
Often considered the most comfortable trimester, this is when many early symptoms ease. The fetus grows significantly — by week 20, most women can feel fetal movement (quickening). The anatomy scan ultrasound, typically performed around week 18–22, evaluates fetal development in detail. Glucose screening for gestational diabetes is usually done between weeks 24 and 28. The fetus develops fingerprints, can hear sounds, and begins to practice breathing movements.
Third Trimester (Weeks 27–40)
During the final trimester, the fetus gains weight rapidly and the lungs mature in preparation for breathing outside the womb. The mother may experience back pain, swelling, Braxton Hicks contractions, and difficulty sleeping. Prenatal visits become more frequent — typically every two weeks and then weekly as the due date approaches. Group B streptococcus screening is routinely performed around weeks 35–37. Signs of approaching labor include the baby dropping lower in the pelvis, increased pelvic pressure, and regular contractions.
Key Prenatal Tests and Screenings
Routine prenatal care involves a series of tests to monitor the health of both mother and baby. Blood type and Rh factor testing, complete blood counts, urinalysis, and infectious disease screening are performed early in pregnancy. Ultrasounds track fetal growth and development. Non-invasive prenatal testing (NIPT) can screen for chromosomal abnormalities as early as week 10. Amniocentesis or chorionic villus sampling may be offered if screening results indicate higher risk.
Calculating Your Due Date
The estimated due date is typically calculated using Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period. However, only about 5% of babies are born on their exact due date. First-trimester ultrasound measurements are considered the most accurate method for dating a pregnancy. Due date calculators use these standard formulas to provide an estimate, but the actual delivery date can vary by two weeks or more in either direction.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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