Pregnancy Calendar: First Trimester

Your healthcare professional will confirm your pregnancy, determine the date of conception, and monitor fetal developments during the first twelve weeks. To determine how old the baby is, physicians use the first day of the mother’s last menstrual period, rather than trying to pin down a time of conception. This timeline will give you a better sense of what to expect.

0-4 Weeks


Morning sickness, appetite changes, heightened sense of smell

Fetal Development

Conception, blastocyst development, embryo formation

Prenatal Care

Check for pregnancy at home with a urine test

Schedule an appointment with your physician (most doctors will want to wait until 8-12 weeks for an initial examination)

Causes for Concern

Call your doctor immediately if you experience extreme nausea, fevers, vaginal discomfort or bleeding, leg pains, discomfort during urination, or severe headaches

Delivery Decisions

Talk to your physician about your delivery environment, whether you’ll be giving birth at home, the hospital, or a birthing center

Get referrals for health professionals who will assist during delivery

5-8 Weeks


Continued morning sickness, frequent urination, fatigue

Fetal Development

Formation of the brain, heart, nervous system, head, facial features

Prenatal Care

Between weeks 8 and 18, some doctors will perform an ultrasound to determine conception and due dates; this is more accurate earlier in the pregnancy

Focus on balancing your diet; cravings or appetite loss can affect when and what you eat

9-12 Weeks


Slight growth around your waistline, mood fluctuations, faster hair and nail growth

Fetal Development

Formation of arms, legs, genitals, nails, circulatory system; fetus completely formed at 12 weeks

Prenatal Care

Your first prenatal checkup

  • Physical and pelvic exams
  • Baby screened for potential development and disease risks
  • Physician provides health and lifestyle counseling for upcoming trimesters

First Trimester Screen

  • An optional screening taken between weeks 11 and 13.
  • This in-depth ultrasound screens for chromosomal abnormalities through:
    • Nuchal translucency, a determinant in down syndrome
    • Abnormally high or low hCG (human chorionic gonadotropin, or the “pregnancy hormone) and PAAP-A (pregnancy associated plasma protein a) levels
  • Results may determine whether you require further tests or monitoring in later trimesters.