AFI is part of the BPP and an estimate of the levels of amniotic fluid in the uterus. It is used to measure fetal well-being. The AFI is obtained by performing an ultrasound of the uterus and comparing findings to a chart of percentile values based on gestational age.

1. The pregnant woman lies supine with displacement of the uterus to the left. The abdomen is divided into four quadrants.

2. Ultrasound is used to locate the largest pocket of amniotic fluid in each of the four quadrants, and each pocket is measured vertically. The four values are added together to obtain the AFI. The advantage of this test is that serial follow-up measurements can be done.

1. Oligohydramnios and polyhydramnios are indicators of poor outcome in pregnancy.

2. Oligohydramnios can indicate chronic uteroplacental insufficiency or renal anomaly.

3. An AFI higher than the 97.5 percentile for a certain gestational age is considered to indicate polyhydramnios. Polyhydramnios is associated with upper gastrointestinal tract obstruction or malformation (e.g., tracheoesophageal fistula, hydrops fetalis).

Pretest Patient Care

1. Explain the reason for the AFI procedure.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

False-positive results can occur in a severely dehydrated woman.

Normal

• Average AFI at 20–35 weeks of pregnancy is 8–14 cm. At term, the AFI is usually between 8 and 18 cm. Values < 5 cm indicate oligohydramnios, and those >24 cm indicate polyhydramnios.