Situation: A 22-year-old primigravida registers at the Rural Health Unit (RHU) at 12 weeks' gestation. Before pregnancy she weighed 42 kg, and her height is 152 cm. She has no medical conditions and a single fetus. Her dates are confirmed by a first-trimester ultrasound. At later visits, the same nurse measures her fundal height in centimeters after she empties her bladder: 24 weeks: 23 cm 28 weeks: 27 cm 31 weeks: 30 cm 34 weeks: 30 cm At which visit should the nurse FIRST refer her for an ultrasound to assess fetal growth?

Between 20 and 36 weeks, fundal height in centimeters is about equal to the weeks of gestation, within 2 cm, and it should rise about 1 cm a week. The readings at 24, 28, and 31 weeks are each 1 cm below dates and rising steadily. At 34 weeks, 30 cm is 4 cm below dates and has not grown in 3 weeks, so an ultrasound for growth restriction or low amniotic fluid is needed.

Why the 34-week visit is the first referral point

Between 20 and 36 weeks of gestation, the fundal height measured in centimeters should roughly match the gestational age in weeks, with an accepted variation of about ±2 cm. A single measurement that falls outside this window, or a pattern of slowed growth over serial visits, raises concern for fetal growth restriction or reduced amniotic fluid volume.

For this client, the measurements at 24, 28, and 31 weeks are each only 1 cm below the expected week-based value. These readings remain within the normal ±2 cm range, and the fundal height is still increasing over time. At 34 weeks, however, the measurement is 30 cm, which is 4 cm below the expected 34 cm. More importantly, the value has not changed from the 31-week visit, meaning there has been no measurable growth over a 3-week interval.

A fundal height that is more than 2 cm below the gestational week, especially when combined with a plateau or lack of interval growth, is a clinical trigger for ultrasound evaluation of fetal growth and amniotic fluid. The earlier visits do not meet this threshold because the deficit is small and the trend is still upward.

Key point! Serial trend matters more than a single borderline value. A measurement that is 1 cm below dates but rising steadily is less concerning than a measurement that stops rising, even if the absolute deficit is only slightly larger.

Pathophysiology and clinical rationale

Fundal height reflects the combined contribution of the fetus, amniotic fluid, and uterine size. When fetal growth slows or stops, the fundus fails to rise at the expected rate of approximately 1 cm per week during the third trimester. A plateau over several weeks suggests that the fetus is not gaining weight as expected, or that amniotic fluid volume is decreasing. Both conditions are associated with placental insufficiency, which can compromise fetal oxygenation and nutrient delivery.

Intrauterine growth restriction (IUGR) is a major concern when fundal height lags behind gestational age. Undiagnosed IUGR increases the risk of fetal death, perinatal mortality, and neonatal morbidity. Fundal height measurement is a low-cost screening tool, but it has variable sensitivity depending on the technique used and the population screened. Standardized measurement protocols and plotting on customized growth charts improve detection rates while reducing unnecessary referrals for ultrasound.

The purpose of referral for ultrasound is not only to confirm suspected growth restriction but also to assess amniotic fluid volume, placental appearance, and fetal well-being through biophysical parameters. Ultrasound biometry provides a more direct estimate of fetal weight and can distinguish symmetric from asymmetric growth restriction, which guides further monitoring and timing of delivery.

Watch out! A single low fundal height measurement without a prior trend should prompt repeat measurement or ultrasound, but in this scenario the serial data are available and clearly show the point at which growth stops. The 34-week visit is the first time both criteria—discrepancy beyond 2 cm and absent interval growth—are met.

Visit	Gestational age	Fundal height	Difference from dates	Interval growth	Interpretation
24 weeks	24	23 cm	-1 cm	Not applicable	Within normal range
28 weeks	28	27 cm	-1 cm	+4 cm in 4 weeks	Within normal range, appropriate growth
31 weeks	31	30 cm	-1 cm	+3 cm in 3 weeks	Within normal range, appropriate growth
34 weeks	34	30 cm	-4 cm	0 cm in 3 weeks	Abnormal, requires ultrasound referral

Nursing process application

Assessment of fundal height should be performed with the woman in a supine position after emptying her bladder, using a non-elastic tape measure from the upper border of the symphysis pubis to the top of the uterine fundus along the longitudinal axis of the uterus. Inconsistent technique between visits can produce false readings, so using the same method and, ideally, the same examiner improves reliability.

When a measurement falls outside the expected range or the growth trend flattens, the nurse should verify the measurement, review the gestational age, and consider factors such as maternal body habitus, uterine fibroids, multiple gestation, or fetal position. In this client, the pregnancy is a singleton, dates are confirmed by first-trimester ultrasound, and there are no known medical conditions, so these confounders are less likely.

The decision to refer for ultrasound is based on the combination of a measurement below the expected centile and a failure of the fundal height to increase over consecutive visits. Referral should not be delayed until the next scheduled visit because the risk of ongoing fetal compromise increases with time when growth has plateaued.

Key point! Fundal height screening is most useful when measurements are plotted on a growth chart and interpreted as a trend. A single measurement is less informative than the trajectory over time.