Premature contractions: are they caused by maternal standing?

Area of Science:

• Obstetrics and Gynecology
• Maternal-Fetal Medicine
• Cardiovascular Physiology in Pregnancy

Background:

• Late gestation involves significant physiological changes, including potential circulatory alterations.
• The supine hypotensive syndrome is a known complication, but effects of posture like standing are less understood.

Purpose of the Study:

• To investigate the impact of quiet standing on pelvic venous blood flow and maternal circulation during late pregnancy.
• To determine the relationship between posture, uterine activity, and the potential for uterine compression syndrome (UCS).
• To explore if UCS is more prevalent or earlier in twin pregnancies.

Main Methods:

• Observational study involving 51 women in late gestation.
• Assessment of pelvic vessel compression, venous blood flow, cardiac stroke volume, blood pressure, and heart rate during quiet standing.
• Monitoring of uterine activity and contractions in different positions (standing vs. left recumbent).
• Specific analysis of 9 women with twin pregnancies.

Main Results:

• 33 out of 51 women exhibited phasic uterine compression of pelvic vessels during quiet standing, impeding venous return.
• This led to reduced cardiac stroke volume, decreased systemic blood pressure, and compensatory increased heart rate (9-51 bpm).
• Uterine contractions coincided with circulatory readjustment, suggesting the contracting uterus relieves venous obstruction.
• Uterine activity was significantly higher in the standing position compared to left recumbent in women with UCS.
• All 9 women with twin pregnancies showed UCS with contractions while standing, even earlier in gestation (mean 28 5/7 weeks).

Conclusions:

• Quiet standing can induce uterine compression syndrome (UCS) in late pregnancy by impeding venous blood flow.
• UCS is associated with increased uterine activity, particularly in standing posture.
• Twin pregnancies appear to be at higher risk for developing UCS earlier and more frequently.
• Avoiding quiet standing, especially in twin pregnancies, is recommended to mitigate increased uterine activity and potential circulatory compromise.