“along with Mary.” Tradition states that Joseph walked and Mary rode on a donkey, but there is no evidence of that, it is only tradition. While Mary may have ridden on a donkey, it is also possible she walked. The journey, if down the Jordan Valley and up from Jericho, would have been about 90 miles, while if they traveled the road directly through Samaria, which many people did, would have been about 70 miles. Donkeys were expensive, and while Joseph may have owned one, it is also possible that because Joseph was poor he could not afford to own a donkey (for example, he could not afford a lamb for a birth sacrifice; cp. Luke 2:24).
“had been betrothed.” Matthew 1:20, 24 make it clear that by this time Mary was already Joseph’s wife. Why then does the text emphasize the betrothal here and not the marriage? The answer is because the couple’s union had not yet been consummated; they had not as yet had sexual intercourse (Matt. 1:24-25).
This verse highlights a biblical custom that is hard to see in English. The Greek verb mnesteuō (#3423 μνηστεύω) is in the perfect (past) tense, passive voice. In the ancient Near East, betrothal, the promise of marriage, usually was a contract between the parents of the groom and the parents of the bride. Marriages were arranged, and often many years before the couple was of marriageable age. The perfect tense, passive voice verb shows that the betrothal, the engagement, was something that happened to Mary, not something she did. She did not “get engaged,” her engagement happened to her. This is a much different picture than modern western courtship. The problem with the English translation “had been betrothed” (or “had been engaged”) is that is how we say it when someone used to be (“had been”) betrothed, but is no longer betrothed because the engagement was broken off. Thus it is very hard to produce the truth that is in the Greek text into English without giving the wrong idea. On balance, it seems that communicating that Joseph and Mary were betrothed at the time they traveled to Bethlehem was more important than trying to produce the custom that the engagement had happened to Mary in the past but risk people thinking they were not still engaged.
“was pregnant.” The Greek word is egkuos (#1471 ἔγκυος), a compound word from the preposition en, “in” and the word kuō, the womb. It literally means, “to have in the womb” (Louw-Nida). It simply refers to being pregnant, it does not refer to how far along the pregnancy was. Joseph was a wise and loving man, and wisdom and love would dictate that he would not travel with Mary when she was on the verge of giving birth. While it is true that at the time Mary lived it was difficult to tell exactly when a woman would give birth, if she gave birth on the road that would be exceedingly difficult for the family, so if she had started early contractions or Braxton-Hicks contractions, it is unlikely Joseph would have traveled with her. Actually, since both Joseph and Mary knew the Messiah had to be born in Bethlehem to fulfill the prophecy, and since they had relatives in Bethlehem and were both a “royal” couple who would have been gladly received by many homes, they almost certainly would have allowed plenty of time to be in Bethlehem, at least weeks and very possibly months, before she gave birth.
The King James Version of 1611 AD, and a couple of other English versions, translate egkuos as “great with child.” However, that is an unwarranted translation, because the Greek word simply means, “to have in the womb,” “to be pregnant.” It is likely that the translation in the King James Version was influenced by the Christmas tradition itself, but today, thanks to the work of linguists, historians, and archaeologists, the Greek vocabulary used in the Bible is much better understood than it was 400 years ago, and the modern English versions reflect that fact and just use “pregnant,” or “with child,” which is accurate.