Amniotic Fluid Index and Mean Diastolic Maternal Blood Pressure in Pregnancy-Induced Hypertensive Patients

Abstract

Objective: To determine the correlation between maternal blood pressure value and the volume of amniotic fluid.

Methods: Amniotic fluid index (AFI) and fetal and maternal Doppler, followed by 24-h ambulatory blood pressure were determined in patients with preeclampsia (n = 10), gestational hypertension patients (n = 28), fetal growth retardation (IUGR) (n = 23), and with a healthy normotensive pregnancy (n = 39). Mean 24-h diastolic blood pressure (M24h DBP) was used to describe the overall pressure regimen for each patient. Uteroplacental resistance and fetal peripheral resistance were investigated through color Doppler evaluation of the uterine, umbilical, and middle cerebral arteries.

Results: A significant inverse linear correlation between AFI values and M24h DBP was found for the patients with gestational hypertension (r = −0.45, P <0.005). In the patients with normal uterine resistance (RI), normal fetal growth, and normal Doppler indexes there was a stronger negative correlation (r = -0.66, P < 0.001). No correlation between AFI and M24h DBP was seen in patients with preeclampsia or in those with IUGR, where a redistribution of blood flow with a reduced perfusion of the splanchnic organs was found (umbilical/middle cerebral artery ratio was higher than in the control group, P < 0.001).

Conclusions: In gestational hypertensive patients with no sign of fetal distress, the inverse correlation between AFI and mean 24-h diastolic blood pressure cannot be explained with the redistribution of fetal blood flow. An underlying pathophysiological mechanism involving changes in intracellular electrolyte balance may be responsible for hypertension and AFI reduction.

Key Words:

• Amniotic fluid index
• Hypertension in pregnancy
• Intrauterine growth retardation
• 24-h ambulatory blood pressure monitoring