Is My Mouse Pregnant? High-Frequency Ultrasound Assessment

Summary

High-resolution ultrasound can help streamline experiments requiring timed-pregnant mice by determining the state of pregnancy, gestational age, and pregnancy losses. Presented here is a protocol to illustrate methods to assess mouse pregnancies as well as potential pitfalls (image artifacts) that may mimic pregnancy.

Abstract

The mouse is the mammalian animal model of choice for many human diseases and biological processes. Developmental biology often requires staged-pregnant mice to determine evolving processes at various timepoints. Moreover, optimal and efficient breeding of model mice requires an assessment of timed pregnancies. Most commonly, mice are mated overnight, and the presence of a vaginal plug is determined; however, the positive predictive value of this technique is suboptimal, and one needs to wait to know if the mouse is truly pregnant. High-resolution ultrasound biomicroscopy is an effective and efficient tool for imaging: 1) Whether a mouse is pregnant; 2) What gestational stage the mouse has reached; and 3) Whether there are intrauterine losses. In addition to the embryos and fetuses, the investigator must also recognize common artifacts in the abdominal cavity so as not to mistake these for a gravid uterus. This article provides a protocol for imaging along with illustrative examples.

Introduction

The mouse is the preferred mammalian model for many human diseases and biological processes^1,2,3,4. Research in developmental biology often requires staged-pregnant mice to determine evolving processes at various timepoints^5,6,7,8. Moreover, optimal and effective breeding of model mice requires an assessment of timed pregnancies, particularly when investigators are studying the effects of a gene mutation on develop....

Protocol

All the steps in this protocol follow the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health and have been approved by the Institutional Animal Care and Use Committee of New York University Grossman School of Medicine.

1. Mating of mice for timed pregnancies

1. Pair the appropriate female mouse (usually a heterozygote) in a cage with the appropriate male mouse (usually a heterozygote) for overnight mating.
2. Separate the mice the ne.......

Discussion

The most important first step in the imaging is to identify the vagina and then to determine the bifurcation of the uterine horn to the left and right. By following each uterine horn, the imager is less likely to mis-identify loops of the bowel as the uterus. Moreover, understanding the variations in the appearance of the bowel (with/without fecal matter) is important to distinguish these from the uterus; occasionally, fecal “balls” in bowel loops may mimic a gravid (pregnant) uterus. Although other authors h.......

Materials

Name	Company	Catalog Number	Comments
Depilatory cream
Ethanol, 70%
Fur clippers
Gauze or KimWipes
Isoflurane
Medical oxygen (optional)
Medical tape
Mouse imaging system (including anesthesia set-up and imaging platform)	Fujifilm Visual Sonics	Various	Any system with 40 MHz center-frequency ultrasound transducer probe
Razor blade (not a safety razor)
Scale (to weigh mouse)
Ultrasound gel