First trimester · Pregnancy week by week
Week 4 of pregnancy
Baby is the size of a poppy seed. About 0.04 inches.
By week 4, Black women face a 78% first-trimester prenatal-care utilization rate vs. 88% for white women, per the CDC NCHS data — establishing care now closes that gap. Source
What's happening with the baby
The fertilized egg has implanted in the uterine wall and is now a blastocyst. The amniotic sac and yolk sac form. The neural plate (which becomes the brain and spinal cord) appears. The embryo is roughly the size of a poppy seed — 0.04 inches long.
What's happening for you
You may not feel pregnant yet. A missed period is often the first sign. Some women experience light implantation spotting (lighter and shorter than a period), mild cramping, breast tenderness, fatigue, or heightened sense of smell. Many feel nothing.
Common (normal) symptoms this week
Light implantation spotting (pink/brown, lasting 1–2 days), mild fatigue, breast tenderness, slight nausea, frequent urination starting.
Call your OB or 911 if
- Severe abdominal or one-sided pelvic pain with bleeding — possible ectopic pregnancy.
- Heavy vaginal bleeding (soaking a pad in an hour) with cramping.
- Fainting, severe dizziness, or shoulder-tip pain — ectopic with internal bleeding is an emergency.
- Fever over 101°F with chills or pelvic pain.
- Severe vomiting that prevents keeping any fluids down for 24+ hours (hyperemesis).
Why this week matters for Black families
The first trimester is when prenatal care begins, and the documented disparity in care begins here too. Black women are less likely to receive first-trimester prenatal care (78% vs. 88% for white women per the CDC). Establishing care early — before week 12 — is associated with lower complication rates across the rest of pregnancy. If you're newly pregnant and haven't been seen, call your OB or community health center this week. Adjunctive WIC eligibility means everyone enrolled in Medicaid is automatically eligible for WIC; that's a meaningful first-trimester decision (see WIC by state).
What to do this week
Take a home pregnancy test (most accurate after a missed period). Start a prenatal vitamin with at least 400 mcg folic acid if you aren't already. Schedule a first prenatal visit (most OBs see you between weeks 8 and 10). Avoid alcohol, smoking, and unprescribed medications. Document your last menstrual period (LMP) date — your due date is calculated from this.
References
- ACOG Patient Education: Early Pregnancy. acog.org/womens-health/pregnancy
- CDC NCHS Data Brief 306 — Timing of Prenatal Care.
- USPSTF 2021 Folic Acid recommendation.
Last medically reviewed: .
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