Week 16 of pregnancy

Your baby this week

About 144 g (estimated weight; Source: WHO fetal growth charts (Kiserud et al., PLoS Med 2017)) — about as heavy as a small seb (apple, about 2¾ in across) (Source: USDA SR Legacy (FoodData Central) FDC 171688 'Apples, raw, with skin': portion '1 small (2-3/4" dia)' = 149 g edible portion; SR28 FOOD_DES refuse 10% (Core and stem). As-purchased weight = 149 / (1 - 0.1) = 165.6 g.). Every baby grows a little differently.

How your baby is developing

• Facial muscles are developing, so small expressions like grimacing become possible.UNSW Embryology (CC-BY)
• The circulatory system and urinary tract are typically fully functioning by now.UNSW Embryology (CC-BY)

How you may feel

• The bump is often becoming more visible; standing up quickly can occasionally cause mild dizziness as blood volume increases.NHS
• Some, especially in a subsequent pregnancy, begin to feel the first flutters of movement ('quickening') around now.ACOG

Nutrition this week

• Iron — blood volume rises ~50% — iron demand climbs (Red meat)
• Calcium — fetal skeleton mineralising (Dairy)
• Vitamin D — calcium absorption + bone (Fatty fish)

Tests & scans

• Quad / triple serum screen (if first-trimester screen not done)

When to reach out

• Heavy vaginal bleeding or passing clots.ACOG
• Severe or persistent abdominal or pelvic pain.ACOG
• Severe, persistent nausea or vomiting that prevents keeping any fluids down (possible hyperemesis gravidarum).NHS
• Fever of 38°C (100.4°F) or higher, or chills.WHO
• Severe dizziness, fainting, or a racing/irregular heartbeat.NHS
• Pain or burning when urinating (possible urinary tract infection).NHS
• A severe or persistent headache that doesn't improve.ACOG
• Sudden swelling of the face, hands, or feet.ACOG
• Visual disturbances — blurring, flashing lights, or spots.ACOG
• Fluid leaking or gushing from the vagina (possible ruptured membranes).NHS
• Persistent pain in the upper abdomen, especially under the ribs on the right side.ACOG

These apply to this week specifically. See the full list of urgent warning signs the CDC publishes for pregnancy and the year after birth.