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Amniotic fluid volume estimation in the postdate pregnancy: a comparison of techniques
R L Fischer1, M McDonnell, K W Bianculli
1Department of Obstetrics and Gynecology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Cooper Hospital/University Medical Center, Camden.
Obstetrics and Gynecology
|May 1, 1993
Summary
For postdate pregnancies, a largest vertical pocket of amniotic fluid (AF) less than 2.7 cm best identifies those at risk for adverse perinatal outcomes. This method offers superior diagnostic value compared to other AF volume assessments.
Area of Science:
- Maternal-Fetal Medicine
- Diagnostic Imaging in Obstetrics
- Perinatal Outcomes Research
Background:
- Postdate pregnancy (gestation ≥ 40 weeks) poses risks for adverse perinatal outcomes.
- Accurate estimation of amniotic fluid (AF) volume is crucial for managing these pregnancies.
- Various ultrasound-based methods exist for assessing AF volume, but their diagnostic utility varies.
Purpose of the Study:
- To identify the amniotic fluid volume estimation technique with the highest diagnostic accuracy for predicting perinatal outcomes in postdate pregnancies.
- To compare the effectiveness of different ultrasound measurements in identifying pregnancies at risk.
Main Methods:
- 198 women at ≥ 40 weeks gestation underwent twice-weekly nonstress tests and AF volume assessments.
- Maximal vertical pocket (MVP) and AF index (AFI) were measured and correlated with perinatal outcomes.
- Receiver operating characteristic (ROC) curves were used to determine optimal cutoff values.
Main Results:
- Pregnancies with normal perinatal outcomes had a significantly larger MVP (4.2 ± 1.4 cm) than those with abnormal outcomes (3.2 ± 2.0 cm; P = .02).
- A MVP cutoff of < 2.7 cm was optimal for identifying oligohydramnios, yielding an odds ratio of 7.11 for abnormal outcomes (sensitivity 50.0%, specificity 87.9%).
- The MVP < 2.7 cm threshold demonstrated superior diagnostic value compared to the AFI of 5 cm.
Conclusions:
- A largest vertical pocket (LVP) threshold of 2.7 cm is the most effective ultrasound measurement for identifying postdate pregnancies at risk of adverse perinatal outcomes.
- This LVP cutoff surpasses the diagnostic accuracy of the AF index and the previously used 2-cm LVP rule.
- This finding aids in clinical decision-making for managing high-risk postdate pregnancies.