Important Checkpoints

First Trimester (Weeks 1–13)

  • Weeks 5–8: The Goodell sign (cervical softening) appears around 5 weeks, and the Chadwick sign (bluish coloration of the cervix/vagina) appears around 6 to 8 weeks. The fetal heart rate can first be seen on an ultrasound at 5 to 6 weeks.

  • Weeks 8–10: Human chorionic gonadotropin (hCG) levels reach their peak.

  • Weeks 9–10: Cell-free fetal DNA (cffDNA) maternal blood testing can be performed to screen for trisomy 21.

  • Weeks 10–12: The fetal heart rate becomes audible using a handheld Doppler.

  • Weeks 10–13: Chorionic Villus Sampling (CVS) can be performed to biopsy placental tissue for prenatal genetic diagnosis.

  • Weeks 11–14: Nuchal translucency ultrasound screening is conducted to detect chromosomal and structural abnormalities.

Second Trimester (Weeks 14–26)

  • Weeks 15–20: Amniocentesis is optimally performed to obtain amniotic fluid for definitive genetic diagnosis.

  • Weeks 15–22: Maternal serum alpha-fetoprotein (MSAFP) screening is done to check for neural tube defects and Down syndrome, though the ideal window is 16 to 18 weeks.

  • Weeks 16–18: The Quad screen is performed (includes AFP, inhibin-A, hCG, and estriol).

  • Weeks 16–20: Quickening occurs, which is the pregnant person's first perception of fetal movement.

  • Weeks 18–20: A comprehensive anatomy ultrasound scan is performed to check fetal structures, placental location, and determine sex.

  • Weeks 18–32: During this window, the fundal height measurement in centimeters should directly match the number of gestational weeks.

  • Week 20: The fetus reaches viability, meaning it could potentially survive outside the uterus. The fundus reaches the level of the umbilicus (measuring roughly 20 cm).

  • Weeks 24–28: Gestational diabetes screening is conducted using an oral glucose test.

Third Trimester (Weeks 27–40)

  • Week 28: Anti-D immune globulin (RhoGAM) is administered if the pregnant person is Rh-negative to prevent isoimmunization.

  • Weeks 29–36: Prenatal visits increase in frequency from monthly to every 2 weeks.

  • Weeks 32–36: The RSV vaccine is recommended for pregnant people to protect the infant for up to six months after birth.

  • Weeks 35–37: Group B Streptococcus (GBS) screening is performed using a vaginal and rectal swab.

  • Week 36: The fundus reaches its highest point, resting just below the xiphoid process.

  • Weeks 37–40: Prenatal visits occur every week until birth. Between weeks 38 and 40, the fundal height actually drops as the fetal head engages in the pelvis (lightening).