diff --git a/code/nsfg.py b/code/nsfg.py
index 3d28262f0..40f8e7e30 100644
--- a/code/nsfg.py
+++ b/code/nsfg.py
@@ -65,12 +65,17 @@ def CleanFemPreg(df):
     
     # replace 'not ascertained', 'refused', 'don't know' with NaN
     na_vals = [97, 98, 99]
-    df.birthwgt_lb.replace(na_vals, np.nan, inplace=True)
-    df.birthwgt_oz.replace(na_vals, np.nan, inplace=True)
-    df.hpagelb.replace(na_vals, np.nan, inplace=True)
-
-    df.babysex.replace([7, 9], np.nan, inplace=True)
-    df.nbrnaliv.replace([9], np.nan, inplace=True)
+    df.replace(
+        to_replace={
+            "birthwgt_lb": na_vals,
+            "birthwgt_oz": na_vals,
+            "hpagelb": na_vals,
+            "babysex": [7, 9],
+            "nbrnaliv": [9],
+        },
+        value=np.nan,
+        inplace=True,
+    )
 
     # birthweight is stored in two columns, lbs and oz.
     # convert to a single column in lb