By comparing 180 healthy pregnant women in different trimesters with 45 healthy no-pregnant women in our study, we detected macular choroidal thickness increased during pregnancy. It was consisted with previous reports [4]. Kara, et al. study showed that subfoveal choroidal thickness increased in pregnant women compared with age-matched no-pregnant women [4]. However, Azuma et al. and Rothwell et al. had demonstrated that there was no significant difference in macular choroidal thickness between healthy pregnant and non-pregnant women [15, 16]. Only the pregnant women in the first or third trimester were enrolled in their study might attribute to this contradictory results. As distinct from these studies, we enrolled the pregnant women in each trimesters and performed macular choroidal thickness examination via EDI-OCT.
Our research also found that the most obvious increase of choroidal thickness appeared in the second trimester. It was consisted with GoktaS, et al. report that choroidal thickening could occur at the regions subfoveal, temporal, and nasal to the fovea in the second trimester [5]. Additionally, one study suggested the subfoveal and parafoveal chorodial thickness also increased significantly in second trimester in comparison to the first or third trimester [17]. And, a study conducted by Dadaci, et al. revealed choroidal thickness significantly decreased in the last trimester compared to the first trimester [8]. We considered that blood volume gradually increased at the beginning of pregnancy and a rapid increase occurred in second trimester, after then, slowly increased. Besides, vascular resistance progressively decreased from the fifth week of the gestation that caused blood pressure reduced [5]. The most obvious change of blood volume and vascular resistance occurred in the middle of pregnancy. Therefore, it might be the reason for the increase of choroidal thickness in the second trimester. Pregnancy was been considered a risk factor for CSC that commonly developed in the third trimester. Tan, et al. observed that choroidal thickness increased significantly in patients with acute CSC [18]. We speculated the increased choroidal thickness observed in the second trimester might be the stimulative factor underlying development of CSC in the third trimester.
As we all known, there were no literature about peripapillary choroidal thickness of pregnant women. Previous studies on peripapillary choroidal thickness only been reported in some systemic diseases. Vural, et al [19] found that inferior and nasal peripapillary choroidal thicknesses decreased in patients with vitamin D deficiency. In their study, they thought that a decrease in vitamin D activity in the eye could cause vascular endothelial dysfunction and resulted in choroidal thinning. Patients with multiple sclerosis (MS) showed peripapillary choroidal thinning when compared with healthy subjects in all zones around the optic disc [20]. They considered the decrease of peripapillary choroidal thickness might be secondary to a reduction in blood flow subsequent to RNFL atrophy in MS patients. Therefore, changes in choroidal blood volume might resulted in the dysfunction of photoreceptors and peripapillary choroidal status was important due to the role of choroidal vascularity in the anterior optic nerve [21]. In our study, peripapillary choroidal thickness was thicker in pregnant women with significance for temporal, nasal, nasal inferior, temporal inferior and global quadrant measurement. This result had not been reported before and the significance of this finding has yet to be determined. The precise mechanism for increased peripapillary choroidal thickness at most zones during pregnancy in our study was still unclear nowadays.
The RNFL was the inner retinal layer formed of axons from the retinal ganglion cells, and was the only central nervous system structure which was visible on fundoscopic examination as axons converge in the optic disc [11]. Therefore, it could discover axonal damage and reflected neuroprotection and neurodegeneration. In our study, we found the peripapillary RNFL thickness was thicker at the NS and NI quadrants in normal pregnant women. Tok, et al investigated the effects of severe preeclampsia on RNFL and they found no significant difference between preeclampsia and healthy pregnant women during the pregnancy [11]. In contrast to their study, Neudorfer’s study showed that the RNFL thickness increase in pre-eclamptic patients with abnormal retinal findings compared to the pre-eclamptic patients without abnormal retinal findings [22]. However, there was no control group included healthy pregnant women in their study. At present, we could not find any literature on RNFL measurement in health pregnant women. As we all known, the structures of RNFL not only composed of ganglion cells axons, but also glial and vascular components [23]. Therefore, we could only speculate a thicker RNFL in pregnant women compared to no-pregnant women might caused by pregnant-related vasodilatation. It was reported that the RNFL thickenss also could thicker in preeclampsia because of retinal edema secondary to cerebral edema [22]. Therefore, the change of RNFL thickness might reflect subclinical involvement of the central nervous system in their disease,especially for preeclampsia women. Further studies were needed to investigate this possibility in depth.
Previous researches observed the relationship between choroidal thickness and refractive error, intraocular pressure or axial length and so on [9]. Our study found the subfoveal, temporal and nasal choroidal thickness were all positively correlated with peripapillary choroidal thickness. The subfoveal choroidal thickness was also positively correlated with temporal and nasal choroidal thickness. Additionally, the subfoveal, temporal and nasal choroidal thickness all had positive correlation with peripapillary RNFL thickness at N and NS quadrants. No correlations with subfoveal or peripapillary choroidal thickness were found for CMT. Our results had not been reported before, which indicated that choroid as a whole appeared a tendency of elevation in thickness no matter on macular or optic disk during pregnancy. During pregnancy, vascular resistance decreased due to hormonal change and resulted in reduced blood pressure. The reduction of blood pressure and systemic vascular resistance might explain the increase of the whole choroidal thickness. In addition, one study reported ocular blood flow would increase during pregnancy caused by vasodilation due to estrogen change [5]. Therefore, we considered that these factors would affect both macular and peripapillary choroidal thickness and the choroidal thickness elevation presented a positive correlation between macular and optic disk.
One of our limitations of our study was that we did not evaluate the same pregnant woman from the first trimester to postpartum. A longitudinal study of choroidal thickness could been conducted in further study. Another limitation of our study was that patients of preeclampsia were not enrolled in our study. The change of peripapillary choroidal thickness in preeclampsia was still unknown.