Maternal changes during pregnancy

CO = HR × SV = 80 × 75 mL = 6,000 mL/min = 6.0 L/min.

• Correct: 6.0 L/min:
• 155 mL/min:
• 0.94 L/min:

Minute ventilation is the volume of air moved per minute: tidal volume × breaths per minute.

• The largest volume that can be exhaled after a deepest breath:
• Correct: Tidal volume times breathing rate:
• The air left in the lungs after a normal exhalation:

Progesterone keeps the endometrium intact and the uterine muscle quiet. The placenta takes over making it from the corpus luteum by about weeks 7 to 9.

• Correct: Progesterone:
• Oxytocin:
• FSH:

The heavy uterus can flatten the inferior vena cava against the spine. Less blood returns to the heart, so preload, stroke volume and cardiac output fall, and blood pressure drops. Turning to the left lifts the uterus off the vein.

• Correct: The uterus compressed the inferior vena cava: Correct. Less venous return means less preload and less cardiac output.
• The uterus pressed on the aorta and raised afterload: Pressure on the aorta could lower flow to the legs, but it would not drop her arm blood pressure this way. The key effect is on venous return.
• Lying down triggered a vagal reflex that stopped the heart: Her heart kept beating; she felt faint because her cardiac output fell. The fast recovery on turning shows a mechanical cause.
• Blood pooled in her lungs when she lay flat on the table: Lying flat does not pool blood in the lungs. The problem is blood held back in the lower body.

Pregnancy lowers vascular resistance, which switches on sodium and water retention. The larger plasma volume raises cardiac output and dilutes the red cells. More blood reaches the kidneys, so GFR rises and creatinine falls. Separately, progesterone drives extra breathing, which lowers PCO2.

• Plasma volume: up. The renin–angiotensin–aldosterone system is switched on, so the kidneys keep sodium and water.
• Hematocrit: down. Plasma rises by 40 to 50% but red cell mass by only 20 to 30%, so red cells are diluted.
• Cardiac output: up. Stroke volume rises with the larger blood volume, and heart rate rises too.
• Total peripheral resistance: down. Progesterone and other signals relax arterioles, and the placenta adds a low-resistance bed.
• Glomerular filtration rate: up. Renal plasma flow rises by 50 to 80%, so more is filtered.
• Serum creatinine: down. A higher GFR clears creatinine faster, so its blood level falls.
• Arterial PCO2: down. Progesterone makes the brainstem more sensitive to carbon dioxide, so minute ventilation rises more than metabolism and more carbon dioxide is breathed off.

MAP = CO × TPR. New MAP = 90 × 1.40 × 0.70 = 90 × 0.98 ≈ 88 mm Hg. The fall in resistance slightly outweighs the rise in output.

• About 126 mm Hg: 126 mm Hg counts the 40% rise in cardiac output but ignores the fall in resistance.
• About 108 mm Hg: 108 mm Hg would need a much smaller fall in resistance. With 1.40 × 0.70, the product is just under 1.
• Correct: About 88 mm Hg: Correct. 90 × 0.98 ≈ 88 mm Hg.
• About 63 mm Hg: 63 mm Hg counts the 30% fall in resistance but ignores the rise in cardiac output.

Scarring from an earlier infection can slow the embryo's trip down the tube, so the blastocyst implants in the tube wall. A positive test with one-sided pain, bleeding, no pregnancy in the uterus and slowly rising hCG points to an ectopic pregnancy, which can rupture as it grows.

• A normal early pregnancy too small to see: By 7 weeks with hCG rising, a normal pregnancy inside the uterus is usually visible on ultrasound, and hCG normally doubles every two to three days.
• A placenta previa causing early bleeding: Placenta previa is a placenta over the cervix, a problem of the second half of pregnancy, not of week 7.
• A corpus luteum that has stopped making hCG: The corpus luteum does not make hCG; the trophoblast does. And her hCG is rising.
• Correct: An ectopic pregnancy in a scarred tube: Correct. This picture fits a tubal ectopic pregnancy.

Before birth, high maternal glucose crossed the placenta, and his pancreas adapted by secreting extra insulin, which also made him grow large. Cutting the cord stopped the glucose supply at once, but his pancreas kept secreting extra insulin for a while, so his glucose fell.

• Correct: His extra insulin outlasts the glucose supply: Correct. Extra fetal insulin continues after the glucose supply stops.
• He inherited type 1 diabetes and makes no insulin: Type 1 diabetes causes high glucose, not low, and it does not present at birth.
• Her insulin crossed the placenta and is still acting on him: Maternal insulin is a protein too large to cross the placenta.
• His liver cannot yet store any glycogen for use after birth: A newborn's liver does store glycogen late in pregnancy. The problem is the extra insulin.

Pregnancy raises GFR by about 50%, so creatinine is cleared faster and a normal pregnant value is lower, often about 0.4 to 0.8 mg/dL. A value of 1.0 suggests her filtration has fallen, for example from preeclampsia.

• Creatinine rises in pregnancy, so this value is too low: It is the reverse: creatinine falls in pregnancy.
• Correct: Her GFR should be higher, so creatinine should be lower: Correct. A higher GFR should bring her creatinine down, so a normal-range value hides reduced filtration.
• Creatinine cannot be measured accurately in pregnancy: Creatinine is measured as usual in pregnancy. The issue is reading it against the right range.
• The fetus adds creatinine to her blood, so 1.0 means fetal kidney disease: The fetus's creatinine is small in amount, and a raised maternal value points to the mother's kidneys.

Between weeks 20 and 36, fundal height in centimeters roughly equals the weeks of pregnancy, so about 30 cm is expected. A measurement 8 cm short suggests a small fetus, too little amniotic fluid, or wrong dates, and an ultrasound is needed.

• The fetus is larger than expected: A larger fetus would make the fundal height greater than the weeks, not smaller.
• The measurement is normal for 30 weeks: At 30 weeks, about 30 cm is expected. 22 cm is well short.
• Correct: Slow fetal growth or too little amniotic fluid: Correct. A low fundal height points to slow growth or low fluid.
• She is carrying twins, which crowd each other: Twins would make the uterus larger than expected, not smaller.