Trimesters & Fetal Development: Nursing Guide (+ Cheat Sheet)

Trimesters and fetal development month by month cheat sheet for nursing students and NCLEX prep

Table of Contents

Understanding prenatal care timelines and fetal development is a core competency for OB/Maternity nursing. The NCLEX will absolutely test your knowledge of what labs are drawn in which trimester, what medications are contraindicated, and when major fetal milestones occur.

Use this comprehensive study guide to master prenatal care across all three trimesters, identify teratogenic risks, and track monthly fetal development.

1. Prenatal Care by Trimester

Routine prenatal care is critical for monitoring both maternal and fetal well-being. Here is exactly what happens during each trimester of pregnancy.

1st Trimester (Weeks 0–12) 2nd Trimester (Weeks 13–26) 3rd Trimester (Weeks 27–40)
  • 1st prenatal visit
  • Obstetric history obtained (GTPAL)
  • EDD Calculated (Naegele’s Rule)
  • Ultrasound: abdominal or transvaginal
  • Labs Drawn: CBC, UA, Pap Smear, STIs, HIV, Blood type & Rh factor, Hep B, Rubella titer
  • Fetal heart rate assessed
  • Gestational diabetes screening
  • MSAFP (test for genetic abnormalities)
  • Amniocentesis (if MSAFP abnormal)
  • Abdominal ultrasound
  • Fundal height assessments
  • After 36 weeks, prenatal visits become weekly
  • Rhogam given to Rh-negative patients
  • tDaP vaccine
  • Non-stress tests for high-risk pregnancy
  • Group-B strep test

2. What to AVOID During Pregnancy

NCLEX Safety Alert: Teratogens are substances that can cause physical or functional defects in the human embryo or fetus. Always assess a pregnant patient’s diet, medication list, and daily activities.
Foods & Drinks Medications (Contraindicated) Activities & Environmental
  • Alcohol & Smoking
  • High-mercury foods
  • Unpasteurized dairy & juices
  • Raw foods (meat/fish)
  • High caffeine intake
  • Tetracyclines
  • Warfarin
  • Sulfonamides
  • Anticonvulsants
  • Lithium
  • ACE inhibitors
  • High impact sports & heavy lifting
  • Acupuncture & massage
  • Hot tubs
  • Radiation exposure
  • Changing cat litter (Toxoplasmosis risk)

3. Month-by-Month Fetal Development

Knowing fetal milestones helps you determine if a pregnancy is progressing normally and what to expect during ultrasounds.

Month Key Developmental Milestones
Month 1 Egg turns into embryo; Spinal cord forms.
Month 2 Facial features noticeable; Arms & legs developed; Ultrasound will show gestational sac (Confirms pregnancy).
Month 3 Heartbeat detectable by doppler; Early reflexes present; Faint fetal movements.
Month 4 Gender detectable by ultrasound; Heartbeat detectable by stethoscope; Lanugo starts to form.
Month 5 Passive antibody transfer begins; Fetal sleep patterns evident; Spontaneous fetal movements.
Month 6 Age of viability outside uterus; Lung surfactant begins to develop; Pupils react to light.
Month 7 Alveoli start to mature; Testes descend into scrotum; Surfactant in amniotic fluid.
Month 8 Lanugo starts to diminish; Muscles and bones fully developed; SubQ fat deposited.
Month 9 Fetus very active; Vernix formed; Vertex position (head down).

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