Abdominal Findings in a 16-Week Pregnant Woman
At 16 weeks gestation, the uterine fundus should be palpable approximately midway between the pubic symphysis and the umbilicus, measuring approximately 16 cm on symphysis-fundal height measurement. 1
Expected Physical Examination Findings
Fundal Height Assessment
The symphysis-fundal height (SFH) measured in centimeters should approximately equal the gestational age in weeks between 16 and 36 weeks of gestation. 1
At 16 weeks specifically, the fundus is palpable above the pubic symphysis but has not yet reached the umbilicus (which typically occurs at 20 weeks). 1
Using the traditional landmark method: the uterus becomes palpable above the pubic symphysis at 12 weeks, reaches the umbilicus at approximately 20 weeks, and reaches the xiphisternum at 36 weeks. 1
However, the fundus can be a poor predictor of gestational age and may reach the umbilicus between 15 and 19 weeks, showing significant individual variation. 1
Measurement Technique
SFH should be measured with a tape measure from the top of the pubic symphysis to the top of the uterine fundus in centimeters, not estimated using finger breadths or anatomical landmarks alone. 1, 2
The measurement is most accurate when the patient has an empty bladder and is lying supine with knees slightly flexed. 3, 4
Tape measurement is more reliable than comparing the uterus with anatomical landmarks due to biological variability in landmark placement and disagreement among clinicians on precise relationships between fundus and landmarks. 2
Factors Affecting Measurement Accuracy
Fundal height may be skewed by abdominal distention, increased body mass index, multiple gestation, polyhydramnios, or oligohydramnios. 1
Maternal obesity can affect palpation accuracy, though studies show manual measurements remain reliable even in obese patients when performed correctly. 5
The fetus should be in a longitudinal lie for accurate correlation between SFH and gestational age. 1
Gastrointestinal Changes at 16 Weeks
Progesterone relaxes gastroesophageal sphincters and prolongs intestinal transit times during the second trimester, predisposing to reflux symptoms. 1
These physiological changes affect drug metabolism and gastrointestinal absorption throughout pregnancy. 1
Clinical Significance and Follow-Up
SFH measurement has high sensitivity (78-84%) and specificity (84-88%) for screening low-birthweight-for-gestational-age infants when measured serially. 4
A discrepancy of more than 2-3 cm between measured SFH and expected gestational age warrants further evaluation with ultrasound. 3, 6
If required structures are not adequately demonstrated or if there is size-date discrepancy, ultrasound evaluation is indicated. 1, 5
Common Pitfalls to Avoid
Do not rely solely on anatomical landmarks (umbilicus, xiphisternum) without tape measurement, as this lacks accuracy and reproducibility. 2
Do not use finger breadths as a surrogate for centimeters, as this introduces significant measurement error. 1, 2
Be aware that the coefficient of variation is smallest for SFH compared to abdominal girth or maternal weight gain, making it the most reliable simple clinical parameter. 3
Abdominal wall thickness does not significantly influence SFH measurement accuracy. 3