Statistical analysis
We listed the number of infants with hypospadias in the CH group, PIH group, and control group to estimate the prevalence of hypospadias among pregnancies with or without hypertension. A t-test and single-factor chi-square analysis were used for continuous variables and categorical data,respectively, to screen out potential exposure factors for hypospadias. These exposure factors, which showed significant differences upon single-factor analysis, were included in the follow-up binary logistic regression analysis for categorical variables and the linear regression for continuous variables. The crude regression analysis was conducted to estimate the prevalence of odds ratios (ORs) and 95% confidence intervals (CI) for the associations of hypospadias with the different risk factors in the single-factor analysis. Multivariate regression analysis assessed the independent contribution of these factors to the risk of hypospadias. The Statistical Package for the Social Sciences software (version 25.0) was used to sort out and statistically analyze the relevant data. A significance level of P<0.05 was set for all the tests.
Results
A total of 42,075 pregnancies produced 42,832 male infants from January 2015 to December 2019. There were588 male infants (including three pairs of twins) who had any other deformities except hypospadias, and we excluded these male infants and their mothers (n=585). Finally, 41,490pregnanciesand 42,244 male infants were enrolled (Figure 1). The prevalence of gestational hypertension and hypospadiasis shown in Table 1. In all, 97 newborns were diagnosed with hypospadias, and the overall incidence of hypospadias was 0.23% (97/42,244). Of all the pregnant women, 119(0.29%) had CH, 2,648(6.38%) had PIH, and 38,723(93.33%) had no evidence of hypertensionand were therefore used as the control. The occurrencerate of hypospadias was higher in the PIH group than in the control group (0.944% vs. 0.186%, respectively; RR: 5.08), whereas the occurrence rate in the chronical hypertension group was 0% (Table 1).
The results of the t-test and chi-square test revealed that patients with PIH (25.8% vs. 6.8%), multiple births (17.5% vs. 5.5%), hyperthyroidism (4.1% vs. 0.6%), preterm deliveries (30.9% vs. 9.0%), low-birth-weight (LBW) infants (34.0% vs. 5.1%), and SGA infants (27.8% vs. 2.0%)hada higher incidence of hypospadias than the control participants (P<0.01; Table 2). The influence of the mothers’ age, CH, placenta previa, DM, hypothyroidism, hepatitis B, obesity, amniotic fluid, and use ofin vitro fertilization (IVF)on the prevalence of hypospadias was not significant between groups(P>0.05).
To estimate the contribution of these factors on hypospadias, a binary logistic regression analysis was conducted for categorical variables (PIH, singleton births, hyperthyroidism, SGA), and a linear regression was also carried out for continuous variables (gestational age, birth weight; Table3). These factors still showed a significant relationship with hypospadias in this crude model. However, after adjustment for these potential confounders in a multivariate logistic regression analysis, the results indicated that singleton births (OR: 1.215, 95% CI: 0.672–2.196, P=0.520) and gestational age (OR: 1.138, 95% CI: 0.982–1.319, P=0.087) failed to maintain statistical significance, whereas PIH (OR: 2.437, 95% CI: 1.478–4.016, P<0.01), hyperthyroidism (OR: 4.008, 95% CI: 1.364–11.773, P=0.012), LBW (OR: 0.852, 95%CI: 0.795–0.912, P<0.01), and SGA (OR: 3.282, 95%CI: 1.644–6.549, P<0.01) wereindependent factors that contributed to hypospadias.
Discussion
Prior studies have suggesteda certain relationship between hypertensive disorders in pregnancy and the occurrence of hypospadias in Caucasian populations [11, 12]. However, there is still a lack of large-scale clinical research related to this condition in China. Our study was based on a retrospective cohort study of 41,490 maternal patients and their 42,244newborns, and it found that the occurrence rate of hypospadias also had a significant correlation with PIH inChina. In this study, PIH caused a significant increase in the incidence of hypospadias in male newborns that reached 0.944%, which was about five times as highas the rate in the normotensive pregnancies in the control group (0.186%). Moreover, the statistical analysis showed that the risk of hypospadias caused by PIH was still more than three times as high after multi-factor correction.Interestingly, no newborn with hypospadias was identified in the group with CH in this study, which may have been influenced by the difference in the etiology of these two conditions. CH and PIH share common symptoms of high blood pressure, butthe former is a type of vascular disease that is mostly related with atherosclerosis, psychological factors, or genetic factors, while PIH is typically associated with gestational status and may be caused by placental dysfunction. This study may help explain the potential pathogenesis of hypospadias related with HIP.
The key time window for male reproductive organ development is from 8–14 weeks of gestation during early pregnancy. There is evidence [8] that the morphogenesis of the male reproductive organs depends on a series of hormonal stimulations in which placental-derived hormones play a key role. At first, the human chorionic gonadotropin hormone secreted by the placenta in the early embryo stimulates the differentiation of testicular stromal cells. By the eighth week of pregnancy, testicular stromal cells begin secreting testosterone, which is essential for the normal development of the penis and testes. Therefore, placental dysfunction in early pregnancy could be a possible pathogenic factor for hypospadias. Placental dysfunction was common in patients with PIH [9], which indicated that PIH was relevant to the pathogenesis of hypospadias. In many pregnancies with PIH, especially preeclampsia, early placental function is seriously affected. Hypertension caused by placental spiral, insufficient arterial invasion, luminal contraction and stenosis, or inadequate placental blood flow perfusion may lead to important changes in placental function and consequently affect fetal growth and development [9, 10]. Although PIH is usually diagnosed after 20 weeksof gestation (after the key time window of hypospadias development), the condition may beginlong before 20 weeks, which means that PIH may impact urologic development substantially earlier than it is diagnosed. It is still unknown whether hypospadias occurs secondary to PIH or whether both are outcomes of a common pathogeny. Further genetic or pathologic studies should reveal the potential pathogenesis.
The proportions of hypospadias in LBW and SGA neonates were significantly higher than those in normal-weight neonates. LBW is usuallyrelated with premature delivery, which is a common complication in patients who have hypertensive disorders in pregnancy. A multivariate regression analysis indicated thatgestational age showed no significant relationship with hypospadias after adjustment for confounding factors. However, a decreasing birth weight still increased the incidence of hypospadias in the multivariate regression analysis. In addition, SGA was determined to be an independent risk factor for hypospadias regardless of gestational age. This finding suggested that chronic intrauterine distress might predict the risk of hypospadias in the male fetus despite the gestational age. The birth weight for gestational age could also reflect the condition of fetal growth in the uterus at every stage of gestation; the most intuitive manifestation of fetal growth restriction is that the fetal weight, body length, and biparietal diameter during pregnancy arelower than the normal average [15]. The rate of hypospadias after birth was as high as 1.9% in the group with limited fetal growth during pregnancy[15]. Therefore, fetal weight assessment, body length, and biparietal diameter monitoring during pregnancy can play a vital role in predicting the risk of hypospadias. Our findingsfrom this study may contribute to further information about this condition and a better understanding of how it develops.
The presence ofhyperthyroidism during pregnancy also showed a significantlyincreased risk of hypospadias in newborns in our study. The relationship between neonatal malformations and hyperthyroidism that is treated during pregnancy is still controversial. Most scholars believe that the drugs used to treat hyperthyroidism are more likely to be teratogenic; for example, propylthiouracil is recommended to treat hyperthyroidism during pregnancy [13, 14]. Additionally, the timing of the onset of hyperthyroidism and beginning its associatedmedication may also affect the pathogenesis of hypospadias. Our study showed that the 95% CIsspanned a wide range from 1.364–11.773, which may have decreased the confidence level. Studies with further classification of thyroid diseases and the medications that pregnant women take for themcouldbetter explain their relationship with hypospadias with more certainty.
IVF did not increase the risk of hypospadias in newborns, and this result is consistent with those of previous studies [16]. The risk of hypospadias in the offspring of older women was significantly increased according to the statistics of California Birth Defects Monitoring[17]. However, this present study did not reach a similar conclusion. The statistical results showed that there was no significant difference in maternal age between the two groups.
One limitation of our study was that we did include any information about family history, hormonal medications, exposure to toxic and hazardous substances, or the history of previous abortions. During the process of data collection, we also found that the information we already had might not be correct due to a consideration for the patients’ personal privacy or inadequate medical history collecting. Therefore, to avoid inaccuracies, we did not include these data. Additionally, the classification of hypertensive disorder in pregnancy might need more refinement. Further work may require optimized classifications and a more comprehensive design to provide deep insight into the complex etiology of hypospadias.
Conclusion
Our findings suggested that maternal PIH was an important independent risk factor for hypospadias in Chinese newborns, while CH showed no relationship with hypospadias in the offspring of mothers with PIH. In addition, LBW and SGA (which indicaterestricted growth of the fetus) and hyperthyroidism of the mother werealso significantly associated with hypospadias.