tetrahydrobiopterin (BH4) is degraded by several enzymes, including BH4 oxidase and peroxidases. Several factors can affect its synthesis and degradation. BH4 deficiency or depletion and genetic variations in the genes involved in BH4 metabolism have been associated with hypertension, suggesting that BH4 may play a role in the pathogenesis of hypertension.

The maternity center of Tunis ( CMNT ) is a level 3 maternity center, supporting over 12 000 births yearly, where the caesarean section's rate is very high, close to 45% of deliveries.

Early detection of these patients can help control maternal and neonatal safety outcomes. we can avoid complications such as severe preeclampsia, HELLP syndrom and eclampsia for the mother, and preterm delievery and fetal growth restriction for the new born.

in the literature, studies have reported a decrease in BH4 levels in pregnant women compared to non-pregnant women and others showed that its deficiency or depletion has been associated with hypertension. Moreover, tetrahydrobiopterin administration has been studied as a potential treatment for preeclampsia but the optimal dose has not yet been determined, and further studies are needed to determine the appropriate dose, timing, and duration of BH4 supplementation in this context.

Thus, BH4 blood levels as a mean of screening, could enrich our diagnostic arsenal. The purpose of our study is to compare BH4 levels between preeclamptic and normotensive women.

The investigators will conduct a monocentric , prospective, observational study, including 300 pregnant women (150 normotensive and 150 preeclamptic).

The participants will be divided into 2 equal groups :

• Group P : Preclampsia
• Group N : Normotensive

After written and informed consent are obtained, a standard battery of blood tests including serum BH4 will be runned for the eligible patients at any moment from the admission to the end of the pregnancy.

Baseline data will be collected at enrollment, including demographic and medical history information, blood pressure, proteinuria, and blood samples for BH4 and other biomarker measurements. Follow-up data will be collected at delivery, including blood pressure, proteinuria, and fetal growth measurements, as well as maternal and neonatal outcomes;

After collecting all groups, blood samples will be analysed for BH4.

Inclusion Criteria:

• Women aged over 18 YEARS
• informed consent
• Pregnant
• Term of pregnancy over than 24 weeks of gestation
• Having a normal pregnancy ( for the control group)
• Being diagnosed with preeclampsia or severe preeclampsia as defined in international guidelines (for the case group)

Non- inclusion Criteria:

• Women with known phenylketonuria
• Any history of ( treated or not) hypertension prior to the current pregnancy
• Any history of ( treated or not) diabetes or gestational diabetes during the current pregnancy
• Any history of renal failure or kidney injury) in the current pregnancy
• Women under long-term medications for arterial hypertension or before 24 week of the current pregnancy

300 parturients free from any exclusion criteria , devided equally into 2 groups :

Group P : Preclamptic women : pregnant women in which the diagnosis of preclampsia have been sustaiend

Group N : Normotensive women : pregnant women without any criteria of preeclampsia