Williams Obstetrics: 23rd Edition Study Guide Williams Obstetrics, 23rd Edition Study Guide is the only study guide keyed to the field's premier text, Williams Obstetrics, 23rd Edition. Essential for your preparation for any obstetrics exam, this unmatched study guide delivers everything you need for the most thorough review possible. The 23rd edition features a new full-color design, more than 350 images incorporated as question material, and the addition of clinical case questions to test your decision-making skills and ability to apply the content to real-world situations.