Today our topic of discussion is Use of Ultrasound in Obstetrics.
Use of Ultrasound in Obstetrics
Use of Ultrasound in Obstetrics
Sonography is a noninvasive procedure and has been proved safe to the conceptus, even with repeated exposures at any stage of pregnancy (Dutta, 2001). Routine sonography in early months is used for:
- Diagnosis of pregnancy: Detects gestational ring at 5th week, fetal poles and gestational sac at 6th week, cardiac pulsation at 7th week and embryonic movements at 8th week of gestation
- Detection of abnormal conceptus prior to clinical manifestations, and fetal malformations
- Accurate determination of gestational age is possible, which is helpful later in pregnancy when IUGR is suspected.
- For this, crown-rump length (CRL) at 10-11 weeks gives the best predictive value
- Diagnosis of twins can be made early in pregnancy effective management
- To diagnose unsuspected placenta previa: Because of the possibility of placental migration to the upper segment, repeat scanning should be performed later- around 34th week
Selective sonography is done when indicated at any time during pregnancy for the following reasons:
- To determine the maturity of the fetus: Crown-rump length (CRL), biparietal diameter (BDP) and femur length (FL) are the measurements of choice for assessment of gestational age. Determination of the maturity is important in cases of:
- Uncertain gestational age
- Discrepancy between amenorrhea and uterine size
- Prior to elective induction for postmaturity or elective cesarean section. Suspicion of fetal and/or placental abnormalities such as:
- Suspected ectopic pregnancy Blighted ovum (empty sac)
- Incomplete abortion
- Hydatidiform mole
- Localization of placenta as in placenta previa Abruptio placentae
- Intrauterine growth retardation
- Intrauterine death
- Malpresentations, such as breech, transverse or face
- Structural defects, such as neural tube defects, absent or abnormal limbs
- Defects of gastrointestinal, and urinary system, and heart defects
- Prior to invasive procedures such as chorion villus biopsy, amniocentesis, cordocentesis, photocopy and intrauterine fetal therapy
- As a part of antepartum or intrapartum fetal surveillance a biophysical profile
- Integrity of a previous cesarean scar-a weak scar or placental implantation over the scar can be detected
- Postpartum period: Secondary PPH
- Retained placental bits
- Subinvolution due to fibromyoma
- Neonatal head screening to diagnose:
- Intraventricular hemorrhage
- Hydrocephalus.
Transvaginal Ultrasonography
Transvaginal ultrasonography (TUS) is usually done during the first trimester of pregnancy. As the transducer is closer to the object, the images are of enhanced quality. A full bladder is not required. Transvaginal sonography is superior to transabdominal sonography in diagnosing placenta previa (Fig. 33.12).
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