Trimester-by-Trimester Pregnancy Guide

What's Happening with Your Baby

The embryo develops all major organs during weeks 6–10 — this is the most critical window for fetal development. By week 12, your baby is about 2 inches long and all limbs are formed. The heart is beating, reflexes are developing, and facial features are taking shape. The placenta is now fully functional.

Common First Trimester Symptoms

• Morning sickness — nausea/vomiting affecting 70–80% of pregnant women, typically peaks at 8–10 weeks and resolves by 14 weeks
• Fatigue — extreme tiredness as your body produces progesterone and blood volume increases by 50%
• Breast tenderness — hormonal changes cause sensitivity, fullness, and nipple darkening
• Frequent urination — kidneys process more blood; uterus presses on bladder
• Light spotting — implantation bleeding (week 4–6) is common; any red bleeding should be reported to your provider
• Food aversions and cravings — smell sensitivity is particularly heightened

Prenatal Appointments & Tests (First Trimester)

• First OB visit (8–10 weeks): confirm pregnancy, calculate due date, review medical history, bloodwork, Pap smear if due
• Cell-free fetal DNA / NIPT (10–13 weeks): optional blood test screening for chromosomal conditions (Down syndrome, Trisomy 18/13)
• First trimester combined screen (11–13 weeks): nuchal translucency ultrasound + blood tests (hCG, PAPP-A) for chromosomal risk assessment
• CVS (10–13 weeks): diagnostic test (not screening) for those with high-risk results or carrier status

What's Happening with Your Baby

The "honeymoon" trimester — nausea typically subsides, energy returns, and you'll start to show. Baby grows from 3 inches to about 14 inches and starts to look distinctly human. Hearing develops by week 18; most mothers feel the first kicks ("quickening") at 18–25 weeks. Baby can swallow, hiccup, and respond to light by week 26.

Common Second Trimester Symptoms

• Round ligament pain — sharp, brief pains in lower abdomen as the uterus grows; normal but worth mentioning to your provider
• Nasal congestion — "pregnancy rhinitis" affects 30% of women; saline spray is safe
• Heartburn / reflux — uterus displaces stomach; eat smaller meals, avoid lying down after eating
• Back pain — growing belly shifts center of gravity; prenatal yoga and proper posture help
• Leg cramps — especially at night; may be related to calcium/magnesium levels
• Feeling baby move — typically first felt at 18–25 weeks (earlier in second pregnancies)

Prenatal Appointments & Tests (Second Trimester)

• Anatomy scan / Level 2 ultrasound (18–20 weeks): detailed survey of all fetal structures, placenta location, amniotic fluid, and sometimes sex determination
• Amniocentesis (15–20 weeks): diagnostic (not screening) for chromosomal or genetic conditions; offered to high-risk pregnancies or those with abnormal screening
• Glucose challenge test (24–28 weeks): 1-hour test to screen for gestational diabetes; if abnormal, 3-hour glucose tolerance test follows
• Prenatal visits every 4 weeks — blood pressure, weight, fundal height measurement, fetal heart rate

What's Happening with Your Baby

Baby goes from 2 lbs to 7–8 lbs average (up to 10+ lbs). Lungs mature — the critical developmental milestone for premature survival. Brain triples in weight during the third trimester. Baby gains protective fat layer, drops into head-down position (typically by 36 weeks), and all systems prepare for life outside the womb.

Common Third Trimester Symptoms

• Braxton Hicks contractions — irregular, painless "practice" contractions; distinguish from real labor by timing regularity and whether they ease with rest/hydration
• Shortness of breath — baby pushes up on diaphragm; usually improves when baby "drops" (lightening) at 36–38 weeks
• Insomnia — discomfort, frequent urination, and anxiety make sleep difficult; left-side sleeping is recommended
• Swollen feet and ankles — normal edema; call your provider if sudden/severe or accompanied by headache
• Pelvic pressure — baby settles deeper as engagement approaches; "lightning crotch" (sharp vulvar pain) is common

Prenatal Appointments & Tests (Third Trimester)

• Every 2 weeks (28–36 weeks), then weekly (36–40 weeks)
• Group B Strep (GBS) test (35–37 weeks): vaginal/rectal swab; if positive, IV antibiotics during labor
• Fetal position check (36 weeks): confirm baby is head-down; if breech, discuss external cephalic version (ECV) or C-section planning
• Biophysical profile (BPP) or non-stress test (NST): ordered for high-risk pregnancies or post-dates (40+ weeks) to assess fetal wellbeing
• Cervical checks (as needed): assess dilation and effacement as you approach your due date

Signs of True Labor vs. False Labor

Go to the hospital / birth center if: contractions are 5 minutes apart lasting 60 seconds for 1 hour (5-1-1 rule), your water breaks, you have heavy bleeding, or fetal movement has significantly decreased.

What to Expect After Birth

The "fourth trimester" is a major transition for your body and mind. Normal postpartum experiences include: lochia (vaginal discharge lasting 4–6 weeks), perineal soreness (vaginal delivery) or incision pain (C-section), uterine cramping ("afterpains") as the uterus contracts — worse with breastfeeding, engorged breasts around days 3–5, night sweats and hormone fluctuations, and significant emotional shifts.

Baby Blues vs. Postpartum Depression

• Baby blues (80% of mothers): weepiness, mood swings, anxiety, starting 2–3 days after birth and resolving within 2 weeks — normal hormonal adjustment
• Postpartum depression (1 in 7 mothers): persistent sadness, inability to bond, hopelessness, or anxiety lasting beyond 2 weeks — requires treatment
• Postpartum anxiety: racing thoughts, excessive worry, physical tension — equally common as PPD, less recognized
• Postpartum psychosis (rare, 0.1%): hallucinations, delusions, confusion — psychiatric emergency, call 911