Preeclampsia is a pregnancy-specific disorder characterized by hypertension and dysfunction of several organs, that is associated with maternal and fetal complications. The human gut microbiota is related to health and disease including hypertension. Alterations in gut microbiota composition can change the short-chain fatty acid profile released by the bacteria and contribute to hypertension and metabolic syndrome. It is unclear if the composition of the gut microbiota is altered in women who develop late-onset preeclampsia. In this study, we investigated the composition of the gut microbiota at 28 weeks gestation in women who developed late-onset (>34 weeks gestation) preeclampsia (DPE) by 16S rRNA gene amplicon sequencing of fecal samples obtained from 213 pregnant women in the SPRING cohort (Study of Probiotics IN Gestational diabetes). Quantitative real-time PCR was used to assess the density of butyrate-producing genes. Gut microbiota composition was compared between women with and without DPE. The abundance of the butyrate-producing Coprococcus genus significantly decreased in DPE. Abundance of Coprococcus is significantly and positively correlated with the abundance of genes encoding the terminal step in bacterial butyrate formation (but and buk). Women with DPE also had significantly reduced levels of serum butyrate prior to the development of symptoms than controls. This study suggests that a reduction in the abundance of butyrate-producing bacteria, and Coprococcus spp. in particular, may contribute to an increased risk of developing preeclampsia in pregnant women.