What can a B-ultrasound examination at 36 weeks of pregnancy determine?

Mar 12, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

The 36-week pregnancy ultrasound is an important prenatal examination during the third trimester. It helps assess fetal growth and development, fetal position, amniotic fluid volume, placental maturity, and umbilical blood flow. By measuring indicators such as the fetal biparietal diameter, head circumference, abdominal circumference, and femur length, the ultrasound can evaluate whether the fetal weight and development are consistent with the gestational age.

　　The B-ultrasound examination at 36 weeks of pregnancy is an important prenatal checkup during the late stages of pregnancy. It enables assessment of the fetus's growth and development, fetal position, amniotic fluid volume, placental maturity, and umbilical blood flow. If there are any concerns, it is recommended to seek medical advice in advance. Detailed analysis is as follows:

　　1. Fetal growth and development: By measuring indicators such as the fetal biparietal diameter, head circumference, abdominal circumference, and femur length, the fetus's weight and development can be evaluated to determine whether they align with the gestational age, thus understanding the intrauterine growth status of the fetus.

　　2. Fetal position: Determining the position of the fetus in the uterus, whether cephalic, breech, or transverse, helps in selecting the mode of delivery. A cephalic position is considered a normal fetal position, which is favorable for vaginal delivery; breech or transverse positions may necessitate consideration of cesarean section.

　　3. Amniotic fluid volume: Observing the depth and index of amniotic fluid to assess whether the volume is normal. Both excessive and insufficient amniotic fluid may adversely affect the fetus, such as fetal distress and preterm birth.

　　4. Placental maturity: Assessing whether placental function is normal. Placental maturity is divided into four grades; at 36 weeks of pregnancy, placental maturity is generally grade II or III. Premature or delayed placental maturation may affect nutrient supply and oxygen delivery to the fetus.

　　5. Umbilical blood flow: Monitoring the umbilical artery blood flow of the fetus to evaluate the blood supply status of the fetus in the uterus. Abnormal umbilical blood flow may indicate problems such as intrauterine hypoxia or poor placental function.

　　If the examination results show abnormalities, pregnant women should consult a doctor promptly and take appropriate measures to ensure the safety of both mother and baby.

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What does it mean if no gestational sac is seen on B-ultrasound examination?

A B-ultrasound examination failing to detect a gestational sac may indicate technical limitations, an examination performed too early, delayed embryonic development, ectopic pregnancy, or maternal conditions such as uterine fibroids. The absence of a gestational sac on B-ultrasound does not necessarily mean pregnancy failure; a comprehensive assessment combining serum hCG levels, clinical symptoms, and follow-up results is necessary. If there are no abnormalities such as abdominal pain or bleeding after the examination, a follow-up check may be scheduled after an interval as directed by a physician.

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What tests are needed for patients with hydatidiform mole?

In general, hydatidiform mole is a gestational trophoblastic disease. Patients need to undergo examinations such as B-ultrasound, serum human chorionic gonadotropin (hCG) testing, fetal heart rate monitoring, X-ray examination, and histological examination. Before undergoing these examinations, patients should inform their doctors about their medical history, symptoms, and other relevant information, so that doctors can better formulate treatment plans.

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Can drinking water one hour before an ultrasound increase amniotic fluid?

In general, drinking water one hour before a B-ultrasound does not increase amniotic fluid, as there is no direct connection between the two. If the examination reveals low amniotic fluid levels, adjustments should be made under a doctor's guidance through long-term regular hydration and nutritional supplementation. Simply drinking water temporarily before the exam will not help. Before undergoing a B-ultrasound, you should drink an appropriate amount of water in advance according to the requirements of the specific area being examined.

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What should I do if there is excessive gas in the abdomen during a B-ultrasound examination?

Excessive abdominal gas observed on B-ultrasound may be caused by improper diet, excessive air swallowing, constipation, gastritis, irritable bowel syndrome, etc. It can be improved by adjusting diet, improving eating habits, medication, and regulating intestinal function. If excessive gas persistently affects the examination or is accompanied by worsening abdominal pain or bloating, prompt medical attention is necessary.