The prevalence of myopia is seemingly increasing, and it is one of the major causes of blindness. High myopia is defined as a refractive error with spherical equivalent exceeding -6 diopters and/or the axial length longer than 26.5 mm. The global prevalence of high myopia is estimated to rise from 2.7% of the world population in 2010 to 9.8% of the world population in 2050. High myopia is characterized by axial length elongation, and consequent stretching of the posterior eye wall (thin retina and choroid). There are many complications of high myopia such as posterior staphyloma, lacquer cracks and myopic choroidal neovascularization. Normal labour may cause the ocular complication in pregnant women with high myopia, such as macular hemorrhage. Therefore, the caesarean section with epidural anesthesia is recommended. Moreover, there is no standard screening guideline for pregnant women with high myopia.

There are few studies of posterior ocular changes during pregnancy. A recent meta-analysis showed that the choroidal thickness and retinal vascular density were increased during pregnancy especially in the 3rd trimester. From the literature review, there is only one publication of physiologic ocular changes during pregnancy in high myopia. Chen et al demonstrated that the choroidal thickness was increased significantly in the 3rd trimester. However, the changes of retinal vascular density in pregnant women with high myopia have never been studied before.

Inclusion Criteria:

• age > 18 years
• high myopia: spherical equivalent > 6 diopters and/or axial length > 26.5 mm
• singleton pregnancy
• clear ocular media
• written inform consent

Exclusion Criteria:

• high risk pregnancy such as pre-eclampsia, gestational diabetes mellitus, hyperthyroidism and asthma.
• history of retinal diseases such as macular edema and retinal vascular occlusion
• history of intraocular inflammation or endophthalmitis
• history of intraocular laser treatment
• history of intraocular surgery

Withdrawal criteria

• childbirth before 34 weeks' gestation
• multifetal pregnancy was detected by ultrasound
• high risk pregnancy which could not follow the research protocol such as severe pre-eclampsia
• retinal diseases occur during the follow-up period such as central serous chorioretinopathy, retinal detachment and choroidal neovascularization
• significant ocular trauma during the follow-up period
• severe peripartum or postpartum complications such as thromboembolic disease and postpartum hemorrhage