Uterine Palpability and FSH Levels at 4 Months Gestation
At 4 months (16 weeks) gestation in a G2 patient, the uterine fundus is palpable approximately midway between the pubic symphysis and umbilicus, and FSH levels are suppressed to undetectable or very low levels during pregnancy.
Uterine Fundal Height at 4 Months Gestation
The uterus becomes palpable above the pubic symphysis at 12 weeks gestation and reaches the level of the umbilicus at 20 weeks. 1 At 16 weeks (4 months), the fundus should be palpable approximately halfway between these two landmarks.
Expected Clinical Findings:
- The fundus is reliably palpable abdominally at this gestational age 1
- The symphysis-fundal height measurement becomes clinically reliable between 16-36 weeks gestation, when the height in centimeters approximately corresponds to gestational age in weeks 1
- At 16 weeks, expect the fundal height to measure approximately 16 cm from the pubic symphysis 1
Important Clinical Considerations:
- Body habitus significantly affects fundal height assessment - abdominal distention and increased body mass index reduce reliability of fundal height as a predictor of gestational age 1
- Multiple gestations and non-longitudinal fetal lie can make fundal height measurements less reliable 1
- The uterus size at this stage is approximately that of a small melon and clearly extends above the pelvic brim 2
FSH Levels During Pregnancy
FSH is suppressed to undetectable or very low levels throughout pregnancy and has no clinical role in routine antenatal assessment. 3, 4
Physiological Basis:
- FSH's primary role is to stimulate folliculogenesis and formation of pre-ovulatory follicles 3
- During pregnancy, the hypothalamic-pituitary-ovarian axis is suppressed by high levels of estrogen, progesterone, and human chorionic gonadotropin (hCG) 3
- FSH measurement has no diagnostic or monitoring value during established pregnancy 4
Clinical Pitfall to Avoid:
- Do not order FSH levels during pregnancy - this test is used for assessing ovarian reserve, diagnosing menopause, or evaluating infertility, not for monitoring pregnancy 3, 4
- The relevant hormone for pregnancy monitoring at this stage is hCG, which should show a gestational sac on ultrasound well before 16 weeks 5
Recommended Clinical Assessment at 16 Weeks
Initiate symphysis-fundal height measurements starting at this gestational age and continue serially at every antenatal visit. 1
Standard Assessment Protocol:
- Measure fundal height using a tape measure from the pubic symphysis to the top of the uterine fundus 1
- Plot measurements on customized growth charts rather than population-based charts 1
- Trigger ultrasound evaluation if fundal height is >3 cm less than gestational age in weeks 1
- Trigger ultrasound if fundal height shows slow or static growth (change <5 mm over 14 days) 1