As the mortality of patients with IAH is higher than those without IAH, surveillance and early management of IAH is increasingly implemented in these IAH-prone patients. Pregnancy have physiologic progressive IAP elevation usually close to the diagnostic threshold of IAH in the third trimester [12]. Acute intra-abdominal inflammation due to acute pancreatitis developing in the third trimester definitely has an effect on IAP. In this study, IAH was observed in all the third trimester pregnancy diagnosed with MSAP or SAP. The incidence of IAH in pregnancy was 82.4 %, which was higher than our previous study in the non-pregnancy pancreatitis group (around 65 %, 39/60) [13] but there was no significant difference (p = 0.24, χ2 test). The likely reason was the abdominal wall which was already strained by the enlarged uterus had less ability to tolerant any rapid increase of IAP. The difference need to be observed with more samples in each group in the future.

Previous reports showed the main cause of AP in pregnancy was biliary disease [14, 15]. It is generally mild yet it tends to recur [15]. Notably, most severe cases tend to be hyperlipidemic pancreatitis [5, 16]. Normal pregnancy is known to have physiological hyperlipidemia. It is thought to represent a generalized increase in substrate mobilization both for the placenta and the growing fetus. Clinically significant hyperlipidemia characteristically occurs in the third trimester when lipid clearance is outpaced by lipid synthesis and release. Pancratitis, only with triglyceride levels above 11.3 mmol/L, is defined as hyperlipidemic pancreatitis [17]. In the present study, nearly 50 % patients (8/17) met the diagnostic criteria of hyperlipidemic pancreatitis. Except one patient with MSAP, the other seven patients were diagnosed as SAP. Severe obesity is one kind of reason of increased IAP. In this group the mean BMI on addition was near the ideal range of pregnant BMI according to the 2009 Institute of Medicine guidelines [18].

Table 3 shows the distribution of IAH in different classifications of AP in pregnancy. All the patients with MSAP or SAP manifested different grades of IAH (100 %), including two cases manifesting ACS. Significantly increased IAP could reduce intra-abdominal organ perfusion and contribute to deterioration in organ function [2, 3]. Histological and ultra-structural analysis of the pancreas in a porcine model of IAH showed that IAH might worsen the pancreatitis [19]. Similarly, both SAP and IAH had been demonstrated remarkable negative effects on systematic hemodynamics, oxygenation and organ function in porcine models [20]. Consistent with these results, in this study, IAP had been showed to significantly correlate with maternal APACHE II score (r = 0.7456, p = 0.0006). In addition, it was reported that mortality in acute pancreatitis patients with ACS was 49 % versus 11 % without ACS [9]. Fortunately, all women in this study survived, though two cases had ACS. These women might benefit from the prompt and effective decrease of IAP by CS.

In pregnant ewes, increased IAP (10 mm Hg for 30 min followed by 15 mm Hg for 30 min) caused reduced uterine blood flow and fetal hypoxemia [21]. Similarly, in our study, 1-min Apgar score and umbilical cord artery pH, as the indexes of hypoxic and ischemic injuries of the fetus [22], were negatively correlated with IAP (r = −0.7465, p = 0.0034; r = −8232, p = 0.0005; respectively). Furthermore, the IAP of cases with live infants was significant lower than that of those patients with non-viable pregnancies. A particularly high perinatal mortality of nearly 30 % was observed in this study. Cases with SAP manifesting severe IAH had to undergo termination of pregnancy and/or pancreatic debridement for irreversible signs of fetal distress or continued instability of the mother after the admission.

Recent data suggest that the adverse effects of elevated IAP can occur at much lower levels than previously thought [23]. In this study, devastating consequences to both mother and fetus occurred at an IAP of less than 20 mm Hg, a value which was common and well tolerated in non-pregnant patients with SAP [1, 24]. Unfortunately, intrauterine fetal death occurred in three cases with IAP of more than 19 mm Hg. Therefore, for pregnant women with AP in the third trimester, continued surveillance and early management of IAH as soon as IAP higher than 15 mm Hg may be beneficial to not only protect the mother from further detrimental effects, but also to decrease perinatal mortality.

The general strategies suggested to lower IAP include evacuating intra-luminal contents, evacuating intra-abdominal space occupying lesions, improving abdominal wall compliance, optimizing fluid administration, optimizing systemic and regional tissue perfusion, or as a last resort, decompressive laparotomy [25]. Considering that the expanding uterus in the last trimester occupies most of the intra-abdominal space, the most prompt and effective means to decrease IAP may be the delivery of the fetus (via CS) when the IAP is persistently elevated and a threat to maternal/fetal health. Delivery of the fetus can early avoid excessive negative stimulation to fetus by the acute raised IAP, and might decrease the perinatal mortality. Further case–control studies are needed to confirm these associations. CS is prompt and effective in reducing the intra-abdominal volume as well as moving fetus away from the severe physiologic derangements of the mother. As CS is not a normal delivery method, its indication should be explored further. In the present study, most women with SAP required delivery of the fetus. Even with moderate IAH, CS is the preferred option for delivery. However, it is unfortunate that the IAP of mothers post-delivery has not been monitored regularly and the effect of CS on IAP could not be further qualified. Another limitation of our study is that the abdominal perfusion pressure (mean arterial pressure minus intra-abdominal pressure) was not analyzed which would be an important index of the effects of IAH on organ perfusion. Further studies focused on utero-placental blood supply will be beneficial for the improvement of perinatal mortality.