Earliest Visualization of Pregnancy Structures on Ultrasound

Timeline of Early Pregnancy Ultrasound Findings

A gestational sac can be visualized on transvaginal ultrasound at approximately 5 weeks gestational age, with the embryo typically visible at 6 weeks gestational age, as recommended by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2
The yolk sac is visualized at approximately 5½ weeks gestational age, and is a critical finding for confirming pregnancy, according to the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2
An embryo with cardiac activity is typically visualized on TVUS at 6 weeks gestational age, with a strength of evidence rated as high by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2, 3
The amnion is typically visualized on TVUS at approximately 7 weeks gestational age, as reported by the American College of Radiology 1, 3

Before visualization of a yolk sac or embryo, an intrauterine fluid collection should be reported as a "probable gestational sac" or "probable pregnancy", as stated by the American College of Obstetricians and Gynecologists 2
The presence of a yolk sac within an intrauterine fluid collection is incontrovertible evidence of pregnancy, and should be interpreted as a "definite gestational sac" or "definite pregnancy", according to the American College of Obstetricians and Gynecologists 2
Mean sac diameter (MSD) can be used to calculate gestational age before visualization of an embryo, with a moderate strength of evidence, as reported by the American College of Radiology 1, 3
Crown-rump length (CRL) should be used for dating as soon as an embryo is measurable, as it is more accurate than mean sac diameter, with a high strength of evidence, as stated by the American College of Radiology 1, 3

The term "embryo" applies to a conceptus of 10 weeks 6 days gestational age or less, as defined by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2, 3
Beginning at 11 weeks 0 days gestational age, the conceptus should be referred to as a "fetus", as stated by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2, 3
Embryonic or fetal rhythmic pulsations should be reported as "cardiac activity" or "cardiac motion", avoiding terms like "heart motion," "heartbeat," or "heart tones", as recommended by the American College of Radiology 1, 3

Absence of expected structures based on gestational age may indicate poor prognosis, such as absence of yolk sac in a gestational sac >8 mm or absence of embryo in a gestational sac >16 mm, with a moderate strength of evidence, as reported by the American College of Obstetricians and Gynecologists 4
For embryos with CRL <7 mm without cardiac activity, follow-up ultrasound in 7-10 days is recommended, with a moderate strength of evidence, as stated by the American College of Obstetricians and Gynecologists 4
Definitive diagnosis of embryonic demise requires absence of cardiac activity in an embryo ≥7 mm in CRL, with a high strength of evidence, as reported by the American College of Obstetricians and Gynecologists 4

Avoid using terms like "pseudosac" or "pseudogestational sac" as they may lead to clinical errors; instead describe fluid in the endometrial cavity based on its characteristics, as recommended by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2, 5, 4
Fluid in the endometrial cavity with pointed or non-curved margins should be described as "intracavitary fluid" or "fluid in the endometrial cavity", as stated by the American College of Radiology and the American College of Obstetricians and Gynecologists 1, 2