Normal S/D Ratio of Umbilical Artery at 31 Weeks

In daily life, many women experiencing their first pregnancy are unfamiliar with basic reproductive health knowledge. To better assess maternal and fetal health, it is essential to confirm that certain key parameters fall within normal ranges. So, what is the normal S/D ratio of the umbilical artery at 31 weeks’ gestation?

Normal Umbilical Artery S/D Ratio at 31 Weeks’ Gestation

At 31 weeks’ gestation, the normal S/D ratio is generally less than 3. The S/D ratio—short for systolic-to-diastolic ratio—refers to the ratio of the peak systolic velocity (S) to the end-diastolic velocity (D) in umbilical artery blood flow, as measured by color Doppler ultrasound. It is a common and clinically significant parameter used in late pregnancy to evaluate placental resistance and fetal perfusion, and serves as an important indicator for assessing fetal growth and development.

As gestation progresses, the S/D ratio normally decreases gradually—typically by approximately 0.1 per week. An elevated S/D ratio may impair fetal development and often reflects underlying pathological conditions affecting either the mother, the fetus, or both. A high S/D ratio indicates increased resistance in umbilical arterial blood flow, which hinders the transfer of nutrients via the umbilical cord, thereby compromising fetal growth and potentially leading to intrauterine fetal hypoxia. Maternal conditions such as gestational diabetes mellitus or pregnancy-induced hypertension may also contribute to an elevated S/D ratio, posing risks to both pregnancy maintenance and delivery.

During pregnancy, it is advisable to avoid spicy, heavily seasoned, or otherwise irritating foods, and instead consume more fresh fruits and vegetables. Maintain regular work–rest schedules, avoid excessive physical strain, focus on calm and healthy fetal development, and attend all scheduled prenatal check-ups. We hope this information proves helpful!