The reason for this might be due to the fact that complications of pregnancy induced hypertension can cause vascular damage to placenta. This induces the oxytocin receptors, which results in preterm labor and delivery.
Being HIV positive mothers is another factor found to be significantly associated with preterm birth which means that HIV positive mothers were three times delivering their baby at preterm as compared with mothers free from HIV. This finding is in line with a study done in Zahedan, Islamic Republic of Iran, where mothers with infection during pregnancy were more likely to deliver preterm birth baby than without infection [19]. This might be due to the drug effect and immunity of the mother risk factor for preterm birth