Microvascular Changes During Pregnancy Fluctuate Between Trimesters

Microvascular changes during pregnancy are significant between trimesters and compared with individuals who are not pregnant, according to a study published in The Canadian Journal of Ophthalmology.

Researchers conducted a prospective study on data that included 41 eyes of 41 pregnant women (pregnant group; mean age, 30.8±5.9 years) and 45 eyes of 45 nonpregnant women (control group; mean age, 29.7±5.9 years) to investigate potential microvascular changes during pregnancy. The researchers used optical coherence tomography (OCT) and optical coherence tomography angiography (OCT-A) to measure choroidal and retinal blood flow and thicknesses. Measurements evaluated in the study included ocular perfusion pressure (OPP), retinal thickness, choroidal thickness, foveal avascular zone (FAZ) area, superficial and deep capillary plexuses (SCP and DCP, respectively), vessel density (VD), and choriocapillaris (CC) VD. 

Researchers evaluated microvascular changes in pregnant patients between the first, second, and third trimesters. Study participants were between the ages of 20 and 40 years. Data were evaluated using statistical analyses. 

The researchers report no differences in visual acuity, OPP, retinal thickness, and choroidal thickness between trimesters and in the control group. 

During the second and third trimesters of pregnancy, parafoveal inferior retinal thickness measurements increased compared with the first trimester (first trimester, 295.0±44.5 µm; second trimester, 307.6±30.1 µm [P =.037]; third trimester, 307.3±25.0 µm [P =.040]). In the second trimester, central SCP VD measurements increased from 24.2±6.5 µm to 26.8±8.6 µm (P =.163) , but decreased to 21.6±8.2 in the third trimester (P =.01). 

During pregnancy, the SCP FAZ area increased from 260.7±59.0 in the first trimester to  278.1±57.5 in the second trimester (P =.127) and significantly to 299.6±68.6 in the third (P =.011). The central DCP VD increased from 33.1±8.4 µm in the first trimester to 38.4±14.3 in the second trimester (P =.04) and decreased to 24.8±12.8 in the third trimester (P =.002). 

The mean VD measurements of the DCP in all trimesters for both eyes were higher than in the control group, but decreased toward the second trimester (P =.02). CC VD was increased in the third trimester when compared with the second and third trimesters (P <.001). The first and second trimester values were lower than the control group, while the third was higher than the control group (P <.003).

“In our study, peaks in the SCP and DCP VD values were observed especially in the central and temporal quadrants and mean values in the second trimester,” the study authors explain. “We tried to  explain this situation by reviewing the previous studies. In the first of these, it was shown that during uncomplicated pregnancy, blood pressure decreases toward mid-pregnancy and increases to preconception values at term physiologically. In another study, in which retinal vascular parameters were measured at 26 weeks of gestation, the blood pressure was found to be associated with retinal microvascular characteristics, and increased blood pressure during pregnancy caused narrower retinal arterioles, arteriolar branching angles, and a reduced arteriolar fractal dimension.”

Among several study limitations, the estrogen and progesterone levels were not measured in either group, so there is no information about the relationship between hormonal and vascular changes. The follow-up period is longer than in other studies. Overlap of error bars in some figures could indicate that the differences are insignificant.