What is obstetric scan?
Obstetric ultrasound Scan, commonly referred to as an OBS scan, is a vital diagnostic tool used during pregnancy to assess the health and development of the fetus, as well as the maternal anatomy. This imaging technique utilizes high-frequency sound waves to create real-time images of the fetus, placenta, and surrounding structures. The OBS scan plays a crucial role in prenatal care by providing valuable information about fetal growth, anatomy, and well-being, enabling early detection of abnormalities and guiding clinical management.
Purpose of obs scan:
The primary objectives of obstetric ultrasound include:
1.Confirmation of Intrauterine Pregnancy: Obstetric ultrasound confirms the presence of an intrauterine pregnancy, ruling out ectopic or molar pregnancies.
2.Estimation of Gestational Age: Dating ultrasound, typically performed in the first trimester, helps determine the gestational age of the fetus based on measurements such as crown-rump length (CRL).
3.Assessment of Fetal Anatomy: The detailed morphology scan, conducted around 18 to 22 weeks of gestation, evaluates fetal anatomy to detect structural anomalies and ensure normal development.
4.Monitoring Fetal Growth: Serial ultrasounds throughout pregnancy track fetal growth and detect abnormalities such as intrauterine growth restriction (IUGR) or macrosomia.
5.Placental Evaluation: Ultrasound assesses the location, size, thickness, and vascularity of the placenta, identifying conditions like placenta previa or placental abruption.
6.Amniotic Fluid Assessment: Ultrasound measures amniotic fluid volume to detect conditions like polyhydramnios or oligohydramnios.
7.Maternal-Fetal Circulation: Doppler ultrasound evaluates blood flow in the umbilical artery, middle cerebral artery, and ductus venosus to assess fetal well-being and detect signs of fetal distress.
8.Fetal viability: It can confirm the presence of a viable pregnancy and detect early signs of miscarriage or ectopic pregnancy.
9.Fetal position: Ultrasound can determine the fetus’s position in the uterus, which is crucial for planning delivery, especially in cases of breech presentation.
10.Multiple pregnancies: Ultrasound is essential for detecting and monitoring twins or higher-order multiple pregnancies.
Structure of fetus in obs scan:
During an obstetric ultrasound scan, the fetus’s structures typically appear in a sequential order as follows:
1.Gestational sac: The first structure visible early in pregnancy, confirming the presence of an intrauterine pregnancy.It is about 4 to 5 weeks.
2.Yolk sac: Often visible within the gestational sac, providing nourishment to the developing embryo in the early stages. It is about 5 to 6 week.
3.Fetal pole: A small thickening at one end of the gestational sac, representing the early embryo.
4.Fetal heartbeat: Usually detected around 6-7 weeks of gestation, indicating the embryo’s viability.
5.Crown-rump length (CRL): Measurement of the fetus from the top of the head (crown) to the bottom (rump), used to estimate gestational age.
6.Fetal limbs and body: As the pregnancy progresses, the limbs, body, and other fetal structures become more distinguishable.
7.Fetal anatomy: Detailed evaluation of the fetal brain, spine, heart, limbs, and internal organs to assess for any structural abnormalities.
8.Amniotic fluid: Surrounding the fetus, providing protection and cushioning.
9.Placenta and umbilical cord: Assessment of the placental location, size, and function, as well as visualization of the umbilical cord and its insertion into the placenta.
10.Fetal position: Determination of the fetus’s position in the uterus, including whether it is in a head-down (vertex) or breech presentation.
Positions of fetus in obs scan:
During an obstetric ultrasound scan, the fetus can be observed in various positions within the uterus. These positions are essential for assessing fetal presentation and planning for delivery. The main fetal positions observed during an obstetric ultrasound include:
1:Cephalic position: This is the most common and optimal fetal presentation for delivery. In the vertex position, the fetus’s head is down, towards the birth canal, with the buttocks up.
2:Breech position: In this position, the fetus’s buttocks or feet are positioned towards the birth canal, while the head is up, away from the cervix. Breech presentations can be complete, frank, or footling, depending on the position of the fetus’s legs.
3:Oblique position: In this position, the fetus is angled diagonally across the uterus, between the transverse and vertex positions.
4:Transverse position: The fetus lies sideways across the uterus, with its head on one side and its buttocks on the other side. This position is less common and usually not suitable for vaginal delivery.
What is CRL?
Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump).
Measurement of a CRL with fetal cardiac activity is the best measurement for dating purposes.
Accurate through the 12th week of gestation.
What is BPD?
BPD (biparietal diameter), the diameter of your baby’s head. BPD is a transverse or axial image of the fetal head taken at the widest portion of the skull .
Bpd must include the cavum septum pellucidum, thalami, falx cerebri and third ventricle.
BPD: Measure outer table of the skull to the inner table.
HC: Measure around the outer table of the skull.
What is Abdominal circumference?
It is the transverse view at the level of stomach bubble portal sinus, supine of the fetus.It measures diameter from outer to outer.
It reflects more of fetal size and weight rather than age.
Position of placenta in obs scan:
During an obstetric ultrasound scan, the position of the placenta within the uterus is assessed to evaluate its location and potential impact on the pregnancy. The main placental positions observed during an obstetric ultrasound include:
1.Anterior placenta: The placenta is located on the front wall of the uterus, closest to the mother’s abdomen. This position is common and usually not associated with any complications unless it covers the cervix which is called Placenta privia.
2.Posterior placenta: The placenta is located on the back wall of the uterus, closest to the mother’s spine. This position is also common and is considered favorable for childbirth as it does not interfere with the baby’s descent through the birth canal.
3.Fundal placenta: The placenta is located at the top of the uterus, near the mother’s ribcage. This position is also favorable for childbirth.
4.Lateral placenta: The placenta is located on one side of the uterus, either to the left or right. This position is less common but usually not associated with complications.
5.Low-lying placenta: The placenta is located in the lower segment of the uterus, near or partially covering the cervix. This condition is known as placenta previa and may require close monitoring during pregnancy, as it can increase the risk of bleeding and complications during childbirth.
6.Placenta accreta: The placenta is abnormally attached to the uterine wall, potentially invading into the muscle layer. This condition can increase the risk of severe bleeding during childbirth and may require special management.
Anomilies of fetus in obs scan:
Fetal anomalies detectable via ultrasound include:
1. Neural tube defects: Such as spina bifida or anencephaly.
2.Heart defects: Like atrial septal defects or tetralogy of Fallot.
3.Limb abnormalities: Such as clubfoot or missing limbs.
4.Abdominal wall defects: Including gastroschisis or omphalocele.
5.Craniofacial anomalies: Like cleft lip or palate.
6.Genitourinary abnormalities: Such as hydronephrosis or polycystic kidneys.
7. Chromosomal abnormalities: Like Down syndrome or Edward syndrome.
8.Central nervous system anomalies: Including hydrocephalus or holoprosencephaly.
9.Skeletal anomalies: Such as osteogenesis imperfecta or skeletal dysplasia.
10.Gastrointestinal anomalies: Like esophageal atresia or duodenal atresia.
