The risk factors that differed significantly between groups D and ND were mostly consistent with those found in previous studies [7–10, 14]. The risk factors for pregnancy-associated dilatation or dissection are a large sinus of Valsalva, rapid growth of the sinus of Valsalva during pregnancy, moderate to severe aortic valve or mitral valve regurgitation, and family history of sudden death or aortic dissection [7–10, 15].

According to the relatively large prospective study of Meijboom et al. [16], pregnancy in women with Marfan syndrome seems to be relatively safe up to an aortic root diameter of 45 mm. Also, Canadian guidelines [23] recommend that women with an aortic root diameter beyond 44 mm should be strongly discouraged from becoming pregnant. In a case report of a patient who developed a massive retrograde type B aortic dissection 7 days after normal spontaneous vaginal delivery, Gandhi et al. [24] described the patient as “petite” (body surface area, 1.69 m²); however, in case of smaller physics such as Asian and Japanese woman, the cutoff value for regarding avoidance of pregnancy may be a sinus of Valsalva diameter ≥40 mm, rather than ≥45 mm.

The diameter of the sinus of Valsalva adjusted for body surface area (diameter of the Valsalva/body surface area, mm/m²) may be more appropriate for selection of high-risk cases before pregnancy. The relative aortic size was first used to predict complications in patients with thoracic aortic aneurysms [18]. An aortic size index (ASI) ≥25 mm/m² in the first trimester is possibly a risk factor for aortic dilatation or dissection during pregnancy and postpartum. The ASI is a novel measurement of relative aortic size that predicts rupture of aortic aneurysm [18], and Davies et al. found that the ASI was more important than absolute aortic size in predicting aortic complications, especially in smaller women [18]. There was more rapid growth of the sinus of Valsalva in patients with Marfan syndrome with pregnancy-associated aortic dilatation or dissection, compared to those without these conditions. Therefore, even if the diameter of the sinus of the Valsalva is small, rapid growth carries a risk of aortic dissection or dilatation. The same phenomenon has been reported in nonpregnant cases of Marfan syndrome. Meijboom et al. [25] followed 108 women with Marfan syndrome and aortic root growth prospectively using serial echocardiograms and found that the patients could be divided into two normally distributed groups based on aortic growth rates: 90 % were slow growers and 10 % were fast growers. Higher incidence of dissections of the ascending aorta (25 % vs. 4 %, P < 0.001) is observed in the fast growers, and the average growth of the sinus of Valsalva in the fast group was 1.8 mm/year. The median growth in the five dissected cases was as high as 4.1 mm/year [12 ]. This larger increase relative to that in Meijboom et al. [16] is probably due to the influence of hemodynamic change including increased blood volume, heart rate, and stroke volume during pregnancy. Furthermore, hormonally mediated histological changes also occur in the aorta, including a decrease in mucopolysaccharides and loss of elastic fibers in the aortic wall [26–28]. Therefore, care is required in treating patients with a high growth rate of the sinus of Valsalva. The frequency and degree of aortic and mitral valve regurgitation were also higher in cases with aortic dilatation or dissection, and these valvular changes may have positive impact on dilatation or dissection.