MONTREAL -- Women who experienced early miscarriage were associated with lower levels of blood flow to the uterus, a small observational study found here.
The 10 women (out of 56 examined) who experienced early pregnancy losses were associated with reduced prepregnancy levels of uterine blood flow (P<0.001), as well as a lower "uterine index" -- calculated as uterine blood flow divided by cardiac output (P=0.003) than women who had successful pregnancies, , of the University of Vermont in Burlington, reported at the (SRI) annual meeting.
While there was no difference in overall cardiac output between the two groups of women, the women with early pregnancy loss were also associated with a lower brachial pulse wave velocity, though this did not quite reach significance (P=0.07).
, of Stanford University in Palo Alto, Calif., who was not involved with the study, characterized the findings as an "interesting association." He added that placental diffusion is entirely dependent on maternal output, because the placenta does not have a preferential blood flow system, which could be a potential explanation for the association seen here.
"I don't see any practical application for this at this point. Maybe you can increase blood flow to the uterine arteries, but how do you do that?" he told app. "But if you know blood flow to the uterus causes a miscarriage, then you can do something."
McBride and her team decided to examine the mechanisms behind early pregnancy loss, as half of all pregnancy losses are due to genetic abnormalities of the embryo.
"We believe that despite similar cardiac outputs, the lower uterine index seen in these women reveals a physiologic difference in the way blood flow is directed, resulting in less blood flow available to sustain a pregnancy in women who later suffer loss," she said at the presentation. "This may represent a pre-pregnancy hemodynamic phenotype where cardiac output is directed away from the uterus to other organs and may also speak to the bidirectional interplay between uterine blood flow and endometrial receptivity."
In fact, women who suffered a prior miscarriage were more likely to have subsequent miscarriages if they had "reduced" uterine blood flow (OR 1.14 per ml uterine blood flow, P=0.02) and a slower brachial pulse wave velocity (OR 7.69 per m/sec, P=0.02).
McBride and colleagues also found that the lower the levels of uterine blood flow, the earlier the pregnancy loss occurred, with 22% of the relationship explained by uterine blood flow.
Reduced uterine blood flow also appeared to play a role in the women who had successful pregnancies, as out of the 10 women with low uterine blood flow and a successful pregnancy, seven reported having a history of early prior loss or taking more than 1 year to conceive.
"Women who later experience early pregnancy loss may have a localized uterine environment which is less receptive for sustaining pregnancy," said McBride. "This may point to a causal reason for many unexplained early pregnancy losses."
Primary Source
Society for Reproductive Investigation
McBride CA, et al "Reduced uterine blood flow in the non-pregnant state contributes to subsequent early pregnancy loss" SRI 2016; Abstract O-016.