Content area

Full Text

 
Headnote

Abstract

Aims: The present study aimed to determine whether yolk sacs with abnormal sonographic appearance are associated with adverse perinatal outcomes in both early and late gestation. Matherial and methods: A total of 305 viable singleton pregnancies with gestational age of 6 to 9 weeks were prospectively evaluated with respect to perinatal outcomes and sonographic characteristics of the yolk sacs. Results: An abnormal yolk sac was found in 66 pregnancies. In pregnancies with enlarged yolk sacs a miscarriage occurred in 37.5% of cases (3/8). The pregnancies with a yolk sac diameter ≥ 5 mm had a significantly higher risk of miscarriage (p = 0.005). The risk of miscarriage was statistically similar between the pregnancies with regular and those with irregular yolk sacs (p = 0.73). Miscarriage occurred in 3.8% of pregnancies with irregular yolk sacs (2/52) and none of pregnancies with echogenic yolk sacs (0/6). Adverse perinatal outcomes were not associated with either irregular or echogenic yolk sacs. Conclusions: An enlarged yolk sac visualized before the 7th week of gestation is strongly associated with a significantly increased risk for spontaneous miscarriage. The presence of an echogenic or irregular yolk sac appears to be unrelated to adverse perinatal outcome.

Keywords: yolk sac, pregnancy, ultrasound, first trimester, miscarriage.

Introduction

The yolk sac acts as the primary route of exchange between the human embryo and the mother before the placental circulation is established. The yolk sac pro- vides nutritional, metabolic, endocrine, immunologic, and hematopoietic functions during organogenesis in em- bryonic life, and is considered to reach its highest level of functional activity between the 4th and 7th week of embry- onic development [1].

The yolk sac is a critical landmark that identifies a true gestational sac [2]. In fact, it is the first conceptional structure that is usually visualized by transvaginal so- nography when a gestational sac measures over 8 mm. Sonography shows the yolk sac as a round structure that is made up of an anechoic center bordered by a regular well-defined echogenic rim. The diameter of a yolk sac is usually 3-4 mm and increases in size up to the 10th or 11th week of gestation [3].

It has been hypothesized that abnormal sonographic findings related to the size, shape and internal structure of...

Show less