Lesson 1, Topic 1
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Fetal Heart Tones

June 23, 2023

Fetal Heart Tones

The fetal heart shows activity by the 7th week of gestation. Practitioners can auscultate fetal heart tones between 10 and 12 weeks with Doppler scan (Figure 25-1). To hear the fetal heart tones, place the instrument in the midline, just above the symphysis pubis, and apply firm pressure. Some difficulty may be seen in locating heart tones in obese women during the early stages. Offer the woman and her family the opportunity to listen to the fetal heart tones. Fetal heart tones (FHTs) are to be assessed for a full minute. The rate and characteristics of the tones should be evaluated. FHTs are assessed at each visit the expectant mother has for the remainder of the pregnancy.

Fundal Height

During the second trimester, the growing uterus rises from the pelvic cavity and becomes an abdominal organ. The top portion of the uterus is referred to as the fundus. The fundal height, or measurement of the height of the uterus above the symphysis pubis, is one indicator of fetal growth. McDonald’s method is commonly used. The measurement also provides a gross estimate of the duration of pregnancy. When the fundal

Table 25-2 Assessment Tools to Evaluate Fetal Well-Being

DIAGNOSTIC TEST OR ASSESSMENT TOOL

DESCRIPTION AND PURPOSE

Ultrasound scan (US)

High-frequency sound waves visualize fetus to help determine gestational age, monitor fetal growth, visualize number of fetuses and location of placenta, estimate volume of amniotic fluid, note presence of anomalies.

Maternal serum alpha-fetoprotein (AFP) screening

Blood test to identify birth defects and anomalies such as Down syndrome (low levels) or neural tube defect (high levels).

Chorionic villus sampling (CVS)

Aspiration of small amount of tissue from the placenta to detect genetic disorders.

Amniocentesis

Aspiration of small amount of amniotic fluid to reveal sex and chromosomal abnormalities, health status, and maturity of fetus. Performed at 16th week of pregnancy to detect abnormalities; performed later in pregnancy to determine fetal lung maturity.

Nonstress test (NST)

Fetal movement and fetal heart rate recorded with external fetal monitors to evaluate the response of the fetal heart rate to fetal movement. Performed when risk is present for placental insufficiency, after the 27th to 30th wk of pregnancy, with stimulation of uterine contractions.

Contraction stress test (CST)

The response of fetal heart rate to decreased oxygen supply during uterine contractions measured via external fetal monitoring. Performed after 32nd wk of pregnancy with stimulation of uterine contractions.

Magnetic resonance imaging (MRI)

Noninvasive tool provides images of soft tissue. Vascular structures within the body may be seen without the use of iodinated contrast medium, without biologic risk. Interference from skeletal, fatty, or gas-filled structures is not a problem as it is in ultrasound scan.

Biophysical profile (BPP)

Fetal status assessment with evaluation of NST, fetal breathing movements, fetal muscle tone, fetal movements, and amniotic fluid volume (see Table 25-3).

Nipple-stimulated contraction test (NST)

Measurement of uterine contractions caused by oxytocin released by the posterior pituitary gland during nipple stimulation. Be careful to avoid hyperstimulation. Contractions longer than 80 sec or more frequent than four in a 10-min period are considered hypertonic. Methods of nipple stimulation include application of warm, moist compresses to the breast tissue and tactile stimulation. Nipple massage for 10 min or twice for 5 min, repeated as necessary, may also be used. Once sufficient contractions to perform the test have occurred, halt the stimulation.

Daily fetal movement count (DFMC; kick count)

Measurement of fetal movement as an indicator of fetal health. Advantages of the test include that it is simple, low cost, noninvasive, and fast. Instruct woman to count fetal movements for 1 hr two or three times daily. No exact number of movements has been identified as a “failing test.” However, fewer than three fetal movements in a 1-hr period or the absence of fetal movements for 12 hr is an indication for further evaluation (see Patient Teaching box on guidelines for counting fetal movements). Daily fetal movement count can be done to evaluate the fetus in high-risk pregnancies for complications related to reduced oxygenation.

Data from Lowdermilk DL, Perry SE: Maternity and women’s health care, ed 9, St. Louis, 2007, Mosby; Druzin M, Gabbe S, Reed K: Antepartum fetal evaluation. In Gabbe S, Niebyl J, Simpson J, editors: Obstetrics: Normal and problem pregnancies, ed 4, New York, 2002, Churchill Livingstone; and Armour K: Antepartum maternal-fetal assessment: Using surveillance to improve maternal and fetal outcomes. AWHONN Lifelines 8(3):232-240, 2004.

height is measured, the woman should be lying flat. Her bladder should be emptied. A paper tape measure or a pelvimeter may be used to measure fundal height. For increased reliability of the measurement, the same person should examine the pregnant woman at each of her prenatal visits. Often this is not possible, so a protocol should be established that specifies the measurement technique, including the woman’s position on the examining table, the measuring device, and the method of measurement used (Figure 25-2).

During the second and third trimesters (weeks 18 to 30), the height of the fundus in centimeters is approximately the same as the number of weeks of gestation. Some maternal characteristics may impact the accuracy of the measurement (Box 25-2). The measurement of fundal height may aid in identification of high-risk factors. A stable or decreased fundal height may indicate intrauterine growth restriction (IUGR); an excessive increase could indicate multifetal gestation or hydramnios (excessive amniotic fluid).