Placental Insufficiency and Oligohydramnios

Definition and Diagnosis

Oligohydramnios is defined as a single deepest vertical pocket of amniotic fluid <2 cm, according to the American College of Obstetricians and Gynecologists 1
In monochorionic diamniotic twin pregnancies, TTTS is characterized by oligohydramnios (DVP ≤2 cm) in the donor twin's sac and polyhydramnios (DVP ≥8 cm) in the recipient twin's sac, as noted by the American College of Obstetricians and Gynecologists 2
Normal amniotic fluid is defined as a Deep Vertical Pocket (DVP) measurement between 2-8 cm, with classifications of oligohydramnios (DVP <2 cm) and polyhydramnios (DVP >8 cm), according to the American College of Radiology 3, 2

Oligohydramnios is commonly associated with Fetal Growth Restriction (FGR), and current guidelines suggest delivery at 34 0/7 to 37 6/7 weeks of gestation for FGR associated with oligohydramnios, as recommended by the American College of Obstetricians and Gynecologists 1
The PORTO study noted that amniotic fluid abnormalities did not independently increase the risk for adverse outcomes in FGR, according to the American College of Obstetricians and Gynecologists 1

Cardiotocography (CTG) is the primary method for fetal surveillance in high-risk pregnancies, and weekly CTG testing after viability is reasonable for FGR without absent/reversed end-diastolic velocity, as recommended by the American College of Obstetricians and Gynecologists 1
Consider biophysical profile (BPP) or modified BPP (NST + amniotic fluid assessment) for fetal surveillance, as suggested by the American College of Radiology 4
Increase frequency of fetal surveillance when oligohydramnios is accompanied by FGR or other comorbidities, according to the American College of Obstetricians and Gynecologists 1
Ultrasound surveillance should begin at 16 weeks of gestation and continue at least every 2 weeks until delivery for twin pregnancies with monochorionic diamniotic placentation, according to the American Journal of Obstetrics and Gynecology 2

For FGR with oligohydramnios, consider delivery between 34 0/7 and 37 6/7 weeks, as recommended by the American College of Obstetricians and Gynecologists 1
For severe early-onset FGR with abnormal Doppler studies, coordinate care between maternal-fetal medicine and neonatology services, according to the American College of Obstetricians and Gynecologists 1
In TTTS, staging and potential interventions such as laser therapy for placental anastomoses may be considered, as noted by the American College of Obstetricians and Gynecologists 2

Increased risk of adverse fetal outcomes, including preterm birth, low birth weight, and low Apgar score, is associated with placental insufficiency and oligohydramnios, although the specific odds ratios are not provided in the cited references 2, 1
Polyhydramnios is independently associated with increased perinatal mortality, with an odds ratio (OR) of 5.8 (95% CI, 3.68-9.11) compared to normal amniotic fluid, and an adjusted OR of 5.5 (95% CI, 4.1-7.6) for fetal demise in non-anomalous singleton pregnancies, according to the American College of Radiology 4
Polyhydramnios is also associated with an independent association with stillbirth (OR, 1.8; 95% CI, 1.4-2.2; P <.001), according to the American College of Radiology 4
The risk of fetal anomalies increases with the severity of polyhydramnios, with approximately 50% of fetuses having anomalies in cases with DVP of 8-9.5 cm, and 88% with DVP ≥16 cm 2
For DVP >8 cm (polyhydramnios), a detailed anatomical survey is warranted, and consideration should be given to fetal echocardiography, screening for maternal diabetes, and TORCH serology to rule out infections 2
Antenatal fetal surveillance is indicated for moderate-to-severe polyhydramnios, according to the American College of Radiology 4
The DVP method has better clinical utility than the AFI method, with fewer false positives and reduced unnecessary interventions, according to the American College of Radiology 4