I think as many posts on this thread illustrate, whether an 18 year old young (unmarried) woman being pregnant in 1986 was a 'scandal,' is largely subjective, and dependent on the individual family, the young woman's culture, the attitude of the neighbourhood, her peers, her religion, her social circle etc...
And there is a fairly significant difference between 1980 and 1989. In 1980 people might have been a little bit more shocked by an 18 year old girl/young woman getting pregnant out of marriage, (as it was just out of the 1970s,) but in 1989 - a few months before the 1990s, many people wouldn't have been shocked really. Not in some social circles and cultures.
1986 is going towards the latter part of the 1980s, so like some others on here, I am also a bit surprised that Debbie's pregnancy was hidden, like it was something shameful. Especially as she was 18, so hardly 'a child...' I don't think Bill and Elaine (Debbie's stepmum) were religious or anything were they? So why was it hidden I wonder?
Basically, there is no right or wrong answer, and clearly some peoples experiences were different to some others. I worked in housing in the late 1980s, and 1990s, and even from around 1987/1988, quite a number of women came in with their 17-20 year old young single pregnant daughter (sometimes they had already had the baby,) to see if she could be put on the list for a house. There didn't appear to be any shame attached to her daughter having a baby/being a single mother.
One of my cousins got pregnant at 19 (in 1987,) by a lad she had been dating for about a year. He ran like the wind when she said she was having a baby, and she just continued to live with my aunt, (her mum) until she met another man when she was 24 and her son was 4 or 5. They got married and had a daughter when her son was 10. Again, no shame or scandal in the mid-late 1980s.
But I understand that in some cultures and families and areas maybe, that it was 'scandalous' for an unmarried woman to fall pregnant, especially if she was under 20. (And obviously, the younger she is, the more of a shock it would be!) 18 like Debbie is doesn't seem like an age where it would be a scandal or a shock (in 1986,) but again, it's all subjective, and dependent on the young woman's family, culture, and religion etc...
I don't think anyone can say it was scandalous as a blanket statement though, or that it wasn't. Because it's all subjective, Certainly wasn't scandalous for an 18 year old young (unmarried) woman to be pregnant where I came from though, in 1986. I do understand though, that people had different experiences.