Condition of Fetal Growth or Malnutrition (Diagnosis) Clinical Trial
Official title:
Sonographic Evaluation of Fetal Growth in the Third Trimester of Low-risk Pregnancy: a Randomized Trial
Sonographic fetal weight estimation at the last weeks of third trimester in low-risk
pregnancies is an effective method for diagnosis of fetal growth restriction (FGR) permitting
close surveillance and timely delivery. The need for a systematic ultrasound evaluation at
the last weeks of a low-risk pregnancy and the best time to perform it remains controversial.
The most commonly used clinical screening tool in this population is the serial measurement
of symphysis-fundus distance, which is a method of a variable and low sensitivity for
detection of FGR.
In Portugal, in accordance with guidelines of Direcção Geral de Saúde from 2015, fetal growth
restriction screening in low risk pregnancies is performed with an ultrasound for fetal
weight estimation at 30th-33rd weeks. Nonetheless, recent data from randomized trials showed
that FGR detection rate was superior at 36 vs 32 weeks' gestation. In cases of severe FGR,
detection rate was also superior at 36 vs 32 weeks' gestation. In a prior retrospective
study, our group analyzed 1429 term low risk pregnancies and the investigators concluded that
small for gestational age term babies (birthweight < 10th centile) had a statistically
significant higher rate of operative deliveries for intrapartum fetal distress than
appropriate for gestational age as well as a higher rate of admission to neonatal intensive
care unit. Moreover the investigators compared the same outcomes within small for gestational
age neonates with antepartum detection at 30th-33rd weeks ultrasound vs undetected (normal
30th-33rd weeks ultrasound). Antepartum detection of small for gestational age neonates
showed a statistically significant lower rate of operative deliveries for intrapartum fetal
distress than undetected small for gestational age neonates. The investigators will conduct a
prospective randomized clinical trial with the aim to evaluate if a 35th-37th weeks after the
standard of care ultrasound in low risk pregnancies is effective in improving the detection
rate of FGR and in reducing cesarean deliveries for intrapartum fetal distress and admission
to neonatal intensive care unit.
The population to include in this study corresponds to the low-risk pregnant women with
surveillance at the Prenatal Consultation or referenced by the Primary Care units to the
Department of Obstetrics & Gynecology of Hospital de Santa Maria. The screening method for
detection of fetuses at risk of fetal growth restriction currently used in low-risk
pregnancies is the measurement of the symphysis-uterine distal distance at all visits from 24
weeks and a third trimester ultrasound at 30-32 (6 / 7 days weeks).
The patients who agree to participate in the study, after signing an informed consent, will
be randomized into 2 groups (with and without an additional ultrasound evaluation at 35-35+6
(6 / 7 days weeks)). The randomization will be done through computer software.
Clinical data will be recorded such as: maternal age, ethnicity, parity, height, weight,
socioeconomic status and smoking habits.
In the study group (ultrasound evaluation at 35-35+6 (6 / 7 days weeks)), the ultrasound
evaluation will include biometric parameters of the fetus: cephalic perimeter, biparietal
diameter, abdominal circumference and femur length. Based on these measurements, the computer
system (Astraia) provides the estimated fetal weight and respective percentile according to
the Hadlock formula. Amniotic fluid will also be measured (maximum column). Functional
evaluation will include: Doppler of the umbilical artery, middle cerebral artery and Uterine
arteries. The respective index of pulsatility and cerebroplacental ratio will be registered.
All Doppler evaluations will be performed in the absence of somatic and respiratory fetal
movements, under transitory maternal apnea, with the lowest insonation angle possible and at
least 3 successive complexes will be evaluated for each measurement.
Obstetric and neonatal outcomes will be registered after delivery by revising medical records
such as: gestational age at delivery, prepartum hemoglobin, type of labor (spontaneous or
induced and respective indication), type of delivery (eutocic, instrumental, antepartum or
intrapartum cesarean section), indication of instrumental or cesarean delivery,
cardiotocographic register characteristics (repeated severe variable decelerations, late
decelerations, absence of variability), evidence of meconial fluid, neonatal morbidity
(hypoglycemia, hypothermia, transient tachypnea, hyperbilirubinemia requiring phototherapy,
meconium aspiration syndrome, admission to neonatal intensive care unit, metabolic acidosis,
intraventricular hemorrhage, necrotizing enterocolitis, sepsis, seizures and asphyxia) and
mortality.
Sample size calculation
According to a retrospective analysis performed in the target population of this study, the
rate of intrapartum fetal hypoxia requiring obstetric intervention in pregnant women with
fetal growth restriction is 28%. Aiming to reduce this adverse perinatal outcome by 10%, it
is estimated that the investigators will need to include a total sample of 2700 pregnant
women (1350 in each group), with 80% power and α level of 0.05.
Performing third-trimester ultrasound at 30-32 weeks, the rate of antenatal detection of
fetal growth restriction is 20.5% in low risk pregnancies. Aiming to increase the detection
rate by at least 7%, the investigators will require a total sample of 1,200 pregnant women
(600 in each group), with 80% power and α level of 0.05. Thus an interim analysis is expected
to be performed when 1200 cases are recruited to the study to compare the detection rate of
fetal growth restriction between the two groups.
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