Preeclampsia remains one of the major causes of maternal and perinatal morbidity and mortality in developing countries where it kills nearly 50,000 women each year [20]. Although its main cause is largely unknown, numerous studies agree on the role played by oxidative stress [24] - [28]. Epidemiological studies show that hyperglycemic disorders occurring during pregnancy are a risk factor for the development of preeclampsia even outside of proven diabetes mellitus [29] [30]. These hyperglycemic disorders linked to the diabetogenic potential of pregnancy are the consequence of the anti-insulinogenic and lipolytic activity of the somatotropic chorionic hormone, prolactin, cortisol and glucagon whose concentrations increase in the second half of gestation [1] - [6]. In 2013, the International Diabetes Federation estimated the overall prevalence of hyperglycemia during pregnancy at 16.9% [12]. To date, several strategies have been used to detect these disorders, including oral provoked hyperglycemia test, fasting glycemia, as well as the determination of glycated hemoglobin HbA1c [38] [39].

In this study, we used fasting glycemia and HbA1c determination. Although the oral hyperglycemia test remains one of the most widely used dynamic tests for the detection of carbohydrate intolerance, the difficulties associated with the supply of anhydrous glucose, its conservation and its cost limited the realization of this test during the present study. Fasting glycemia was measured by the hexokinase method which is a reference method [40]. The threshold value used is that proposed by ADA and adopted by WHO, 92 mg/dl [41]. The results obtained from the HAPO study (Hyperglycaemia and Adverse Pregnancy Outcomes) and those of other studies have shown that this value is the threshold at which maternal glycemia levels are frequently associated with unfavorable pregnancy outcomes [7] [42] [43]. The determination of glycated hemoglobin was carried out by the immunoturbidimetry technique using a COBAS C111 brand analyzer [36] [44]. The choice of the HbA1c dosage is justified by the fact that it reflects the state of glycemia during the 2 to 3 months preceding the measurement [45], its dosage is reproducible and its level is not influenced by the time of blood collection or by fasting status or by any hypo or hyperglycemic treatment [46]. In addition, the oxidative stress generated during the formation of HbA1c would be favorable for the occurrence of preeclampsia and its complications [47] - [51]. In order to avoid errors of interpretation linked to the shortening of the duration of red blood cells, we excluded from this study the cases of sickle cell anemia, the hemoglobinopathy most encountered in our population [52] [53]. The results of the study by Arlène et al. [54] as well as those of many authors indicate that HbA1c is not a reliable indicator in the search for glycemic disorders in subjects suffering from sickle cell anemia. Regarding the reference value of HbA1c used in the present study, although no consensus was found on the reference ranges of HbA1c in healthy pregnant women, the results published by numerous authors indicate that healthy pregnant women have lower HbA1c concentrations than non-pregnant women. O’Kane et al. [55] have suggested HbA1C levels of 5.1%, 4.9% and 5.0% in the first, second and third trimester, respectively, in healthy pregnant women. Nielsen et al. [56] found reference ranges between 4.5 and 5.7% in the first trimester and between 4.4 and 5.6% in the second and third trimester. The results of the study by O’connor et al. [57] showed that the reference values of HbA1c in Caucasian pregnant women were between 4.3 and 5.4% in the first trimester, between 4.4 and 5.4% in the second trimester and between 4.7 and 5.7% in the third trimester. In their study, Versantvoort et al. [58] found HbA1c values in the range of 5.4, 5.5 and 5.8% in healthy pregnant women. These different results obtained in white women are sometimes misinterpreted.

In women of other races given the variability in HbA1c values related to race. We do not have any studies on glycated hemoglobin in pregnant black women. In a large study carried out in Mexico, Sánchez-González et al. [35] determined the HbA1c values of healthy pregnant women in the three trimesters of pregnancy. The calculated reference values were 5.6, 5.5 and 5.7%, respectively in the first, second and third trimester, with an average of 5.6%. We used the average of HbA1c found by Sánchez-González et al., who studied a large multiracial and multiethnic population.

We noted in the present study that the preeclamptic pregnant women had higher fasting blood glucose values compared to the controls (95.0 ± 35.6 mg/dl vs 81.8 ± 17.3 mg/dl, p = 0.006). The proportions of pregnant women with pathological fasting glycemia values (>92 mg%) were however comparable in the two study groups (33.8% vs. 23.9%, p = 0.133).

Higher HbA1c values were observed in preeclamptic pregnant women compared to controls (5.7 ± 1.3% vs 4.8 ± 0.7%, p < 0.001). These higher values of HbA1c in preeclamptic pregnant women were found both in the second trimester (5.7 ± 1.3% vs 4.7 ± 0.6%) and in the third trimester of pregnancy (6.6 ± 0.7% vs 4.8 ± 0.8%). The proportion of pregnant women with pathological HbA1c values (>5.6%) was higher in the group of preeclamptic pregnant women compared to controls (46.5% vs 9.9%, p < 0.001). In the multivariate analysis, an association was established between high HbA1c values and preeclampsia [(OR 6.48 (2.48 - 16.93) p < 0.001].

It appears in the results obtained from the HAPO study and those of other studies than during pregnancy, the risk of maternal and neonatal complications increases linearly with maternal glycemia [7] [42] [43]. Several studies have established an association between the states of maternal hyperglycemia and the occurrence of preeclampsia and its complications [59] [60] [61]. However, the mechanism underlying this association remains less well known. Barden et al. [62] note in their study that insulin resistance is the essential factor in this association. In a large study aimed at identifying the determinants of the association between diabetes mellitus and preeclampsia, Gutaj et al. [63] rather note a very significant positive association between high values of HbA1c in the three trimesters of pregnancy with preeclampsia and its complications. The association between HbA1c levels and adverse pregnancy outcomes remains a large area to explore. Most of the data reported comes from first trimester HbA1c measurements in women with preexisting diabetes [16] [18]. It appears from the numerous studies carried out on pregnant diabetics that high HbA1c values are directly associated with unfavorable pregnancy outcomes and particularly with the occurrence of preeclampsia [64] [65] [66] [67]. Nielsen et al. [65] [66], Damm et al. [68], Tennant et al. [69] note in their studies high levels of HbA1c in pregnant diabetics with preeclampsia compared to non-preclamptics. In the HAPO study, the high levels of HbA1c measured in the second trimester of pregnancy in non-diabetic pregnant women were positively associated with a high prevalence of cesareans, preeclampsia and prematurity [70]. The results obtained from the study by Capula et al. [71] showed that, in pregnant women suffering from carbohydrate intolerance during the second trimester, even if the glycemic values are below the threshold of proven diabetes, the high rates of HbA1c remained strong predictors of adverse obstetric outcomes. In particular, an HbA1c value greater than 5.3% is associated with a 2 times higher risk of occurrence of preeclampsia and neonatal morbidity. In a recent study carried out in New Zealand on 16,122 healthy pregnant women, Hughes et al. [72] showed that an HbA1c level ≥ 5.9% at the start of pregnancy was a clinically relevant marker of the occurrence of preeclampsia, shoulder dystocia and perinatal death. Our results corroborate those of the HAPO study as well as those obtained by Capula et al., then recently by Hugues et al. who note an association between high levels of HbA1c and the occurrence of preeclampsia in pregnant women with unknown diabetes.

It appears from the results of Nielsen et al. [66], that in pregnant women, each increase in the value of HbA1c by 1% above the normal threshold increases the risk of poor perinatal results by 5.5%. This risk is 79% when the HbA1c level is greater than 10.3%. Mané et al. [16] note in their study that in pregnant women without diabetes, an HbA1c level between 5.9% and 6.4% multiplies by 3 the risk of occurrence of preeclampsia and its complications. The results obtained from the study by Cavero-Redondo et al. [73] show that HbA1c is a very reliable indicator of the risk of cardiovascular mortality in diabetics and non-diabetics. In this regard, The National Institute for Health and Clinical Excellence (NICE) [74] [75] recommended an HbA1c level < 6.1% before considering conception in a known diabetic pregnant woman; and this rate must be even lower for an non-diabetic pregnant woman in order to avoid the occurrence of serious obstetric complications, particularly the occurrence of preeclampsia and its complications. Indeed, the oxidative stress generated at all stages of protein glycation and during the formation of HbA1c is favorable to the occurrence of preeclampsia and its complications, making this parameter a true marker of oxidative stress and therefore one of the parameters for assessing the severity and the maternal and fetal prognosis during preeclampsia [47] - [51]. Results obtained from certain studies have shown an association between high levels of HbA1c and anti-angiogenic factors, such as soluble endogline (Seng), implicated in the occurrence of preeclampsia and its complications [31] [76]. In addition, high levels of HbA1c have been shown to favor aggregability and platelet activation, which leads to the release of Thromboxan A2, a potent vasoconstrictor implicated in the pathophysiology of preeclampsia [77]. More recently, studies have demonstrated the role played by HbA1c in the pathophysiology of preeclampsia through the end products of glycation (AGE Advanced glycation end-products). AGEs are a diverse group of reactive molecules that are formed endogenously from intermediate and irreversible glycation products of which HbA1c is a part. These molecules are associated with high concentrations of free oxygen radicals and are responsible for a strong inflammatory reaction, which is thought to be the basis of endothelial dysfunction [78] [79] [80].

The results of numerous studies [81] [82] have shown very high concentrations of AGEs in preeclamptic pregnant women.

We noted during this study that primigestity, primiparity and a history of preeclampsia were risk factors for the onset of the disease. Our results corroborate those published by other authors. Merviel et al. [83] note in their study that primigestity, primiparity, primipaternity as well as personal history of preeclampsia are risk factors for the occurrence of preeclampsia. Similar results are published by English et al. [84] as well as by Cissé et al. [85]. In the study by Gutaj et al. [63], it was noted that the history of nulliparity associated with the high level of HbA1c between 12 - 24 weeks of pregnancy constituted a major risk factor for the occurrence of preeclampsia.

The same is true for the history of primiparity or hypertension associated with high levels of HbA 1c in the three trimesters of pregnancy which constitutes a major risk factor for the occurrence of preeclampsia. It thus emerges from our study that primigestity, primiparity, history of preeclampsia or hypertension are risk factors for the occurrence of preeclampsia. This risk is increased and multiplied by 7 in the presence of high levels of HbA1C measured in the second and third trimester in an unknown diabetic pregnant. In the study by Mohamed et al. [86], it was noted that multigestity was one of the risk factors for the occurrence of preeclampsia. We noted in this study an association between high levels of HbA1c and preeclampsia (OR 6.48 (2.48 - 16.93) p < 0.001), and multigestity (OR 2.94 (1.16 - 7.54) p = 0.007). Although multigestity was not found among the maternal risk factors for preeclampsia in the present study, its association with elevated rates of HbA1c makes this parameter another risk factor for the onset of the disease.

Probably the diabetogenic potential of recurring pregnancies would be the mechanism underlying the association between multigestity and high levels of HbA1c. Twin pregnancy is considered by many authors [87] [88] as one of the risk factors for the occurrence of preeclampsia by more complex mechanisms. The importance of oxidative stress would probably be one of the fundamental mechanisms for the occurrence of preeclampsia in this condition. In this study, we noted a predominance of twin pregnancies among preeclamptic pregnant women. In univariate analysis, we established an association between twin pregnancy and the high values of HbA1c (OR 3.19 (2.83 - 8.22), p = 0.024) and between high values of HbA1c and preeclampsia (OR 7.94 (3.20 - 19.71) p < 0.001). Simmons et al. [89], Dwyer et al. [90] noted in their studies the greater diabetogenic potential associated with twin pregnancy due to the abundant secretion of the somatotropic chorionic hormone, compared to single pregnancy. This makes twin pregnancy a risk factor for the development of gestational diabetes and preeclampsia.

We noted in this study that severe preeclampsia was the most common form, unlike moderate preeclampsia (62% vs 32%). Our observation is similar to that of Cisse C.T et al. [85] who find in developing countries the predominance of severe forms of preeclampsia whose frequency can reach up to 88.7% of cases, according to studies. The results of our study show that eclampsia, acute fetal distress and prematurity were the most common obstetric complications. They were found very significantly in preeclamptic pregnant women with pathological HbA1c values (>5.6%). It appears from the results obtained from the study by Ekbom et al. [91] that the risk of preterm delivery significantly increases with the elevation of HbA1c levels, making this parameter a true predictor of prematurity. Several mechanisms can be evoked to explain the occurrence of these complications in these pregnant women with pathological values of HbA1c, among which the importance of the oxidative stress generated during the formation of HbA1c and its impact on endothelial functioning, influence of anti-angiogenic factors associated with high levels of HbA1c but also the importance of the inflammatory reaction associated with the glycation process.

We noted in this study that preeclamptic pregnancies were characterized by high levels of HbA1c as well as higher values of leukocytes compared to controls (p < 0.001). Liu et al. [92], Wu et al. [93], and Sushma et al. [94] observed high concentrations of inflammation markers in subjects with elevated levels of HbA1c, making HbA1c a marker reliable inflammation [95]. Furthermore, the results of numerous studies show an association between inflammation and preeclampsia [96] [97] [98]. HELLP syndrome (Hemolysis, elevated liver enzymes and low platelet) is another severe complication found in severe forms of preeclampsia [99] [100].

It occurs as a result of endothelial damage associated with the obstruction of intrahepatic micro vessels by microthrombi [101]. It is characterized by hemolysis, elevated liver transaminases and thrombocytopenia. It was noted in the present study that compared to the controls, the preeclamptic pregnant women presented a moderate but very significant elevation of hepatic transaminase levels (GOT 48.3 ± 5.9 IU/L vs 24.3 ± 9.1 IU/L, p = 0.001; GPT 38.6 ± 4.7 IU/L vs 13.8 ± 6.9 IU/L, p = 0.000) as well as a low platelet count (167.8 ± 74.3. 103 elements vs 228.8 ± 56.4.103 vs elements, p < 0.001). Although this study did not establish a relationship between pathological values of HbA1c and the occurrence of this complication, it can be understood that the endothelial dysfunction caused by high levels of HbA1c and by Advanced glycation end-products would be one of the pathophysiological mechanisms. In the study by Asadifar et al. [77], it was shown that high levels of HbA1c also favored aggregability and the platelet activation which would be responsible for the formation of microthrombi and multi visceral attack which can lead HELLP syndrome.

This study is the first to be carried out in Congolese pregnant women. Its weakness lies first, to the small sampling used and the failure to carry out the oral provoked hyperglycemia test in women with pathological values of HbA1c, which would contribute to determining the prevalence of diabetes mellitus, and secondly, the absence of data relating to neonatal parameters on which high levels of HbA1c could have an influence. This prompts us to recommend carrying out a study on a large sampling taking into account all these other aspects.

The strength of this study is to have established in non-diabetic pregnant women, a relationship between the high levels of HbA1c in the second and third trimester of pregnancy with the occurrence of preeclampsia and its complications, which allows to consider this parameter as a bio-marker of oxidative stress and of the appreciation for the maternal and fetal prognosis during preeclampsia. Our results corroborate those published by other authors, and underline the importance of glycemic control during the second and third trimester of pregnancy among the strategies for preventing preeclampsia and its complications.